Twenty-one patients with frontonasal dysplasia were studied. A 2:1 male-to-female sex ratio and increased paternal and maternal ages at the time of conception were found. The significance is uncertain because of small sample size and lack of normal mean values for parental age in Brazil. Apparently, our series is the first to report macrocephaly (six cases). Our series also had a high frequency of patients with agenesis of the corpus callosum (12 cases), basal encephalocele (10 cases), lipoma of the corpus callosum (four cases), and mental deficiency (11 cases). Three patients had the combination of agenesis of the corpus callosum, mental deficiency, and micropenis. It is concluded that frontonasal dysplasia is pathogenetically heterogeneous, representing a regional defect which may not be a single developmental field or sequence. Causal genesis includes a dominantly inherited form, dup(2q), and autosomal recessive Shanske syndrome. Of unknown genesis are two subsets of frontonasal dysplasia patients: 1) the combination of agenesis of the corpus callosum, tibial hypoplasia, and hallucal duplication and 2) ophthalmofrontonasal dysplasia or oculoauriculofrontonasal dysplasia with associated ear tags and epibulbar dermoids.