ABSTRACT OBJECTIVE To examine the effect of seasonality on femoral fracture incidence among people residing in the state of São Paulo, Brazil. METHODS Ecological study based on a consecutive series of 216,348 reports of hospital admissions caused by femoral fractures. A Bayesian statistical model was used for time series analysis, considering the monthly average number of events of femoral fractures per day as a dependent variable. RESULTS Among the female population, significant seasonal effects were observed only for older women, aged 60 years or more. Among younger men (aged less than 20 years) there is not a clear seasonal effect, but among the other age groups there seems to exist a higher number of cases of femoral fractures during the coldest months of the year. CONCLUSIONS In general, more cases of fractures occur during the coldest months of the year; however, men and women have different patterns of incidence according to each age group.