The incidence and distribution of slipped capital femoral epiphysis in Connecticut and in the Southwestern part of the United States were studied. The annual incidence of diagnosed cases among Connecticut residents was estimated to be 3.41 per 100,000 population under age twenty-five, and in New Mexico, 0.71 per 100,000. The ratio of male to female cases in Connecticut, 2.67, was higher than the ratio of 1.70 among Southwestern cases. Median ages at diagnosis were thirteen for males and eleven for females in both regions. Blacks were at greater risk for slipped epiphysis than whites, the annual incidence rates in Connecticut being 7.79 for black males, 6.68 for black females, 4.74 for white males, and 1.64 for white females. Urban-rural differences were slight. In Connecticut, no significant social class gradient was observed, whereas its the Southwest, cases were likely to be residents of poorer communities than controls.