Results from analyses of sex ratios as a function of IQ are presented for 623 autistic children (487 males, 136 females) and 506 nonautistic, communication-handicapped and behavior-disordered children (374 males, 132 females). Proportionately more autistic females were found to have IQs of 34 or below than above 34. However, a linear trend of an increasing number of males with increasing intelligence was found only for nonautistic subjects. The relevance of these findings to genetic factors and the heterogeneity of autism is discussed.