During the 18-year period 1980-1997, 1103 patients were treated as in-patients for slipped capital femoral epiphysis (SCFE) in Scottish hospitals. This paper reports a significant seasonal variation, especially in male patients, with an excess admitted in the autumn. Examining the physiological seasonality of the monthly increment of growth in height and weight in childhood, we hypothesised that these physiological rhythms, while not pathogenetic, may be responsible for the timing of the seasonal features of SCFE. Previously published studies suggest that the average time between first symptoms and diagnosis is 3 to 5 months. The condition may start with the spring peak in growth and become more symptomatic with the autumn peak in weight. In conclusion, we report a new epidemiological finding, but, in accordance with other studies, we cannot provide a certain aetiological explanation. The timing, but not the pathogenesis, of admission to hospital for a SCFE might be related to the timing in the year of seasonal increments of height in spring and weight in autumn. It is tempting to draw attention to associations with environmental features. For example, in autumn there is the most rapid annual fall in temperature, and the hours of darkness are increasing from the autumn equinox to the winter solstice. However, there is no reason to conclude that these associations have anything to do with aetiology.