OBJECTIVE: This co-twin study investigated monozygotic twins who were discordant for schizophrenia for evidence of prenatal growth differences between the affected and well co-twins. METHOD: Four dermatoglyphic markers of prenatal growth were obtained by established procedures from 26 monozygotic twin pairs discordant for schizophrenia, 13 monozygotic twin pairs concordant for schizophrenia, and several normal monozygotic twin samples. RESULTS: The a-b ridge count differences between the affected and well co-twins were greater than those found for concordant and normal monozygotic pairs. In comparison with their well co-twins, the affected twins, in discordant pairs, had developed fewer epidermal ridges in the a-b interdigital area of their right palms. In contrast, no significant differences were found between the affected twins and their well co-twins on markers associated with fetal development before 13 or after 15 weeks estimated gestational age. CONCLUSIONS: Because the a-b ridges are known to complete development between 13 and 15 weeks estimated gestational age, the results provide physical evidence suggesting that the schizophrenia- affected monozygotic twins alone experienced a time-specific and time- limited dysgenesis during this time. Commonalities in the ontogeny of epidermal and neurological structures are discussed.Abstract Teaser