Crouzon syndrome (CS) is an autosomal dominant condition comprising orbital proptosis, midfacial hypoplasia, premature sutural synostosis, and altered proportions of bone lengths in the hands. In families the CS trait is highly variable. Several cases of affected sibs born to unaffected parents have been explained by germinal mosaicism. We hypothesized that cephalometric and metacarpophalangeal analysis may help to classify affected and unaffected subjects within families when clinical diagnosis is difficult. Posterior-anterior and lateral cephalometric radiographs and hand films were taken of 10 CS patients and 18 unaffected relatives. Sixty-two craniofacial and 19 hand linear and angular measurements were made on each subject and standardized by conversion to z-scores using published normal standards. Ten craniofacial variables were selected for use in a stepwise forward discriminant function analysis to develop an equation which could be used to discriminate CS patients from normal subjects. A two-group discriminant function using four craniofacial variables and one hand variable correctly classified the CS patients and relatives 100 % of the time. The results suggest that relatively few facial variables are needed to differentiate most cases of CS but the addition of one or more hand variables may increase the sensitivity. DNA testing is necessary to adequately demonstrate incomplete penetrance in CS, but pretesting subjects for molecular studies using these methods may improve results. Am.