Aim To assess the contribution of a multimodal exercise program on the sleep disturbances (SD) and on the performance of instrumental activities daily living (IADL) in patients with clinical diagnosis of Alzheimer's disease (AD) and Parkinson's disease patients (PD). Methods A total of 42 consecutive patients (23 training group, 19 control group) with PD and 35 demented patients with AD (19 trained group, 16 control group) were recruited. Participants in both training groups carried out three 1‐h sessions per week of a multimodal exercise program for 6 months. The Pfeffer Questionnaire for Instrumental Activities and the Mini‐Sleep Questionnaire were used to assess the effects of the program on IADL and SD respectively. Results Two‐way ancova showed interactions in IADL and SD. Significant improvements were observed for these variables in both intervention groups, and maintenance or worsening was observed in control groups. The analysis of effect size showed these improvements. Conclusion The present study results show that a mild to moderate intensity of multimodal physical exercises carried out on a regular basis over 6 months can contribute to reducing IADL deficits and attenuating SD. Geriatr Gerontol Int 2014; 14: 259–266.