A study of the incidence and distribution of slipped capital femoral epiphysis and a test of the hypothesis that fluorides in drinking water protect against this disease were undertaken in Connecticut and in the Southwestern states of Colorado, Arizona, New Mexico, and Texas. Cases were ascertained by means of diagnostic indices and operating room log books of hospitals, and controls matched to the cases by age, sex, and year of admission were chosen from among 1) patients admitted to orthopedic services of the same hospital as the case, 2) patients admitted to nonorthopedic services of the same hospital as the case, and, in Connecticut, 3) cancer patients reported to the Connecticut Tumor Registry by . Connecticut hospitals.

The annual incidence of diagnosed cases among Connecticut residents was estimated to be 3.37 per 100,000 population under age 25, and in New Mexico, 0.73 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 and mean ages at diagnosis and onset were 13 for males' and 11 for females in both regions. Negroes were at greater risk for slipped epiphysis than whites, the annual incidence rates in Connecticut being 7.79 for Negro males, 6.68 for Negro females 4.74 for white males, and 1.64 for white females.

Urban-rural differences were slight. In Connecticut no social class gradient was observed, whereas in the Southwest cases were likely to be residents of poorer communities than controls. Symptoms began more frequently in spring and summer than in fall and winter among Connecticut patients, while in the Southwest, symptoms were uniformly distributed throughout the year.

In males, left slipped epiphyses occurred twice as often as right, while the two sides were equally frequently affected among females. .About one-fifth of males and one-quarter of females had bilateral involvement. Trauma was said to have precipitated the onset of symptoms in a little less than half of the cases.

Almost two-thirds of the patients were said to be obese, and slightly less than half had weights at or above the 95th percentile for their age. In Connecticut there was an excess of abnormally tall females and of tall and short males, and in the Southwest, an excess of short males. The distributions of heights and weights among Southwestern patients were significantly less than among Connecticut cases.

Charactex-istics present at the time of a first slipped epiphysis which were associated with an increased risk for involvement of the other hip were young age, obesity, being Negro, and not having trauma involved in the onset of symptoms.

Fluorides in drinking water had no demonstrable effect on the incidence of slipped epiphysis, either at levels of 1 ppm artificially fluoridated water, or at levels of 2 ppm or higher.