The effects of testosterone on functional recovery in stroke patients have not previously been studied. The purpose of the study was to determine the effects of pre-rehabilitation serum testosterone levels on functional recovery in male stroke patients. In total, 111 male stroke patients admitted to our department were enrolled in the study (age: 74 ± 10 years, days from stroke onset: 36 ± 14 days). Serum concentration of free testosterone (Free-T) was measured upon admission. Patients were also evaluated using the Functional Independence Measure (FIM) at admission and discharge. The main outcome variable was FIM at discharge. Correlations between Free-T and FIM were evaluated using Spearman's rank-order correlation coefficients. We performed multivariate linear regression analysis to assess the effects of testosterone on functional outcome with adjustment for patient background variables. In addition, we added a subgroup analysis based on age. The average Free-T serum concentration was 4.7 ± 1.7 pg/ml. There was a significant positive correlation between Free-T and discharge FIM. The multivariate linear regression model showed that Free-T concentration was significantly associated with FIM at discharge (β = 0.09; P = 0.01). In the subgroup analysis, Free-T had significant association with discharge FIM only in patients under 76 years old (β = 0.24; P < 0.001). Our data suggest that serum Free-T levels have a positive effect for discharge FIM in male stroke patients.