Because medial epicondylitis has not been studied alone, we investigated its links between personal and occupational factors in repetitive work and its course. A total of 1757 workers were examined by an occupational health physician in 1993-1994. Five hundred ninety-eight of them were reexamined 3 years later. Prevalence was between 4% and 5%, with an annual incidence estimate at 1.5%. Forceful work was a risk factor (odds ratio [OR], 1.95; confidence interval [CI] = 1.15-3.32), but not exposure to repetitive work (OR, 1.11; CI = 0.59-2.10). Workers with medial epicondylitis had a significantly higher prevalence of other work-related upper-limb musculoskeletal disorders (WRMD). Risk factors differed for medial and lateral epicondylitis. The prognosis for medial epicondylitis in this population was good with a 3-year recovery rate at 81%. Medial epicondylitis was clearly associated with forceful work and other upper-limb WRMD, and its prognosis was good.