S o far, the electrical detection of skyrmions in the lattice phase has been achieved only at low temperatures, mainly in magnetic materials with B20 crystal structures 1-7. In this family of materials, contributions to the electrical transport properties are directly linked to the topological nature of skyrmions. Recently, a change in the differential tunnel conductance due to the non-collinearity of single magnetic skyrmions was reported for a PdFe atomic bilayer on Ir(111) 8,9. However, low temperatures preclude the use of magnetic skyrmions in common devices 10-12. The solution can be delivered by engineering magnetic multilayers in the form of stacks composed of ultrathin magnetic layers in contact with heavy-material thin films. Although significant advances have been achieved in the stabilization and current-induced motion of skyrmions at room temperature (RT) 13-17 , until now only imaging techniques have been used to show this 13,18-21. Importantly, no evidence of their detection through purely electrical means has been reported, but this is a crucial prerequisite for any of the potential applications. Here we focus on the transverse Hall resistivity as a sensitive probe for the electrical characterization of magnetic sky-rmions in patterned magnetic multilayer systems. The transverse resistivity ρ xy = V y t/I x (Fig. 1a) is associated with the voltage V y measured across an electrical conductor of thickness t, orthogonal to an applied current I x. In magnetic materials with non-trivial magnetic textures, this transverse resistivity is usually decomposed into three components 22 , = + + xy xy xy xy OHE A HE THE , contributions that arise from the ordinary, the anomalous and the topological Hall effects, respectively. The ordinary Hall effect (OHE) is described by = R H xy OHE 0 , where R 0 is the ordinary Hall coefficient and H ⊥ is the out-of-plane magnetic field component. The anomalous Hall effect (AHE), which contains intrinsic and extrinsic contributions that arise from spin-orbit interactions, can be observed only in materials with broken time-reversal symmetry 22 , as is the case for ferromagnets. The AHE resistivity xy AHE is generally considered as being proportional to the average out-of-plane magnetization, m z , in the sample. The third term is the topological Hall effect (THE) that results from the Berry phase acquired by spin-polarized carriers as they cross a topologically non-trivial magnetic texture, such as skyrmions. In the adiabatic approximation, that is, assuming a strong coupling of the charge with the local spin (which provides an upper-bound estimate), the topological contribution is generally expressed by = PR B xy THE 0 eff , where B eff is the emergent fictitious field in the rest frame of the electrons and P is the magnitude of the spin polarization of the electrons 23. As we recently demonstrated 15 , chiral magnetic skyrmions can be stabilized in multilayers at RT by a large Dzyaloshinskii-Moriya interaction (DMI) that arises at the interfaces of a thin Co layer inserted between two non-magnetic materials. For our study, we selected a similar magnetic multilayered system based on the asym-metric trilayer Pt|Co|Ir with large values of DMI, ranging from 1 to 2 mJ m −2 (refs 24-26). This allows sub-100 nm skyrmions to be stabilized 15,27 as a result of the balance between DMI, magnetic anisot-ropy and exchange coupling 12,28 , as well as the dipolar energy. In the present work, we combined RT electrical-transport measurements with local probe magnetic force microscopy (MFM) imaging, realized concomitantly, on patterned samples with the composition Ta(5)|Pt(10)|[Co(0.8)|Ir(1)|Pt(1)] 20 |Pt(3) (Supplementary Information). A first objective was to control, using large current-density pulses, the generation of small magnetic skyrmions in electron beam (e-beam) lithographed structures (Methods gives the details). Magnetic skyrmions can be generated by the injection of spin-polarized currents through a scanning transmission microscope (STM) tip 29. Another approach is to use inhomogeneous in-plane electrical currents, created by geometrical constrictions, to form bubble skyrmions due to the divergence of the spin torque acting on the magnetic domains walls, as shown by RT magneto-optical Kerr microscopy 13,30. Recently, we reported the thermally assisted nucleation of isolated skyrmions from non-uniform RT magnetiza-tion states in micrometre-sized tracks 21. Here we show how the latter mechanism allows the generation of a finite number of randomly distributed magnetic skyrmions starting from the magnetically saturated state. Fig. 1a shows a schematic view of the experimental setup that allows us to relate the Hall resistivity response directly with the local magnetic configuration in the sample track. The magnetization state Magnetic skyrmions are topologically protected whirling spin textures that can be stabilized in magnetic materials by an asym-metric exchange interaction between neighbouring spins that imposes a fixed chirality. Their small size, together with the robustness against external perturbations, make magnetic skyrmions potential storage bits in a novel generation of memory and logic devices. To this aim, their contribution to the electrical transport properties of a device must be characterized-however, the existing demonstrations are limited to low temperatures and mainly in magnetic materials with a B20 crystal structure. Here we combine concomitant magnetic force microscopy and Hall resistivity measurements to demonstrate the electrical detection of sub-100 nm skyrmions in a multilayered thin film at room temperature. Furthermore, we detect and analyse the Hall signal of a single skyrmion, which indicates that it arises from the anomalous Hall effect with a negligible contribution from the topological Hall effect.