Twenty‐six primary and 21 secondary microcephalics were compared on the criteria of family and birth factors and clinical examinations. The two groups were similar in respect to their birthweights and parental ages at the time of birth. The group characteristics of primary microcrphalics that appear to be useful in distinguishing them from secondary cases are: (1) consanguinity in two of 13 families, (2) significantly increased number (18.9%) of pregnancy losses, (3) almost normal conditions of gestation, delivery and postnatal periods, (4) apparent microcephaly at birth in 50%, (5) relative absence of neurological problems, (6) relatively normal developmental milestones, and (7) increased frequency of subnormal intelligence in first degree relative