Abstract Background Mild cognitive impairment (MCI) affects 10–20% of the individuals over the age of 65; this proportion being higher in the institutional care facilities than within a general population. Aim To assess whether dual-task cost in the individuals affected by MCI depends exclusively on gait, or possibly some other functional capacity components might also come into play, as compared to the healthy controls also remaining in the institutional care. Methods The study was conducted in five nursing facilities, involving 88 subjects in total, i.e. 44 subjects affected by MCI (mean age of 83.8 years; 34 women (77.3%) and 10 men (22.7%), and 44 healthy controls (mean age 81.67 years; 38 women (84.4%) and 7 men (15.6%). Cognitive functions were assessed through Mini–Mental State Examination (MMSE), while gait by Timed Up and Go Test (TUGT). Gait speed was calculated by the 10 Meter Walk Test, and the fear of falling with the Falls Efficacy Scale International. Dual tasks were assessed by TUGT MAN (Timed Up and Go Test Manual) and TUG COG (Timed Up and Go Test Cognitive). Dual Task Cost (DTC) of TUGT MAN and TUGT COG was established. Statistical analyses were completed with STATISTICA Package v. 10. Results Individuals affected by MCI differed significantly from the unaffected ones with regard to their gait test results, when assigned a single-task activity, and dual-task activities, as well as in the gait speed. Dual Task Cost Manual (DTC MAN ) in the MCI group was significantly higher, as compared to the subjects unaffected by MCI. Around 25% of the variance of DTC MAN result regarding the MCI group was accounted for by gait performance in the single-task conditions (TUGT). In the case of Dual Task Cost Cognitive (DTC COG ), this value equalled to approx. 10%. A 1% change in DTC MAN corresponded to approx. 0.5 s change in TUGT, whereas a 1% change in DTC COG entailed approx. 0.35 s change in TUGT walking time. Conclusion Individual functional capacity affected the dual-task performance, especially the motor-motor tasks. Dual-task cost in the subjects affected by MCI was significantly reduced, being more dependent on the gait speed in the motor-motor tasks, which entailed visual memory, than in the motor-cognitive tasks.