Background: Pilot studies suggest potential effects of neck muscle vibration (NMV) and prism adaptation (PA) on postural balance disturbances related to spatial cognition. Objectives: To evaluate the effect of 10 sessions of NMV and/or PA on ML deviation. We used the mediolateral centre of pressure position (ML deviation) as a biomarker for spatial cognition perturbation, hypothesising that PA and NMV would improve ML deviation, with a potential synergistic impact when used together. Methods: We conducted a multicentre, single-blind, randomised controlled study. Participants within 9 months of a right-hemisphere supratentorial stroke and with less than 40% body weight supported on the paretic side in standing were randomised into 4 groups (PA, NMV, PA+NMV, or control). Primary outcome: ML deviation at Day 14. Secondary outcomes: force platform data, balance abilities, autonomy, and ML deviation, measured just after the first session (Day 1), at Day 90, and Day 180. A generalised linear mixed model (GLMM) assessed intervention effects on these outcomes, adjusting for initial ML deviation and incorporating other relevant factors. Results: 89 participants were randomised and data from 80 participants, mean (SD) age 59.2 (10.2) years, mean time since stroke 94 (61) days were analysed. At Day 14, a weak time x group interaction (P = .001, omega-squared = 0.08) was found, with no significant between-group differences in ML deviation (P = .12) or in secondary outcomes (P = .08). Between-group differences were found on Day 1 (P = .03), Day 90 (P = .001) and Day 180 (P < .0001) regardless of age and stroke-related data. On Day 1, ML deviation improved in both the PA and NMV groups (P = .03 and P = .01). In contrast, ML deviation deteriorated in the NMV+PA group on Day 90 and Day 180 (P = .01 and P = .01). Conclusions: The study found no evidence of any beneficial effects of repeated unimodal or combined sessions of NMV and/or PA on ML deviation after stroke. Trial registration: ClinicalTrials.gov identifier NCT01677091.