We aimed to evaluate the impact in sleep quality and musculoskeletal pain of a Medium-Firm Mattress (MFM), and their relationship with objective sleep parameters in a group of institutionalized elders. The sample size included forty older adults with musculoskeletal pain. We did a clinical assessment at baseline and weekly trough the study period of four weeks. We employed the Pittsburgh Sleep Quality Index (PSQI) and Pain Visual Analog Scale (P-VAS). Additionally a sub-group of good sleepers, selected from PSQI baseline evaluation, were studied with actigraphy and randomized to MFM or High Firm Mattress (HFM), in two consecutive nights. We found a significant reduction of cervical, dorsal and lumbar pain. PSQI results did not change. The actigraphy evaluation found a significant shorter sleep onset latency with MFM, and a slightly better, but not statistically significant, sleep efficiency. The medium firmness mattress improved musculoskeletal pain and modified the sleep latency.