The mode of inheritance and the clinical manifestations of amelogenesis imperfecta (AI) were studied in 51 families from the county of Västerbotten, northern Sweden. Autosomal dominant (AD) was the most probable mode of inheritance in 33 families, but X-linked dominant (XD) inheritance was a possible alternative in one family. Autosomal recessive (AR) inheritance was found likely in 6 and X-linked recessive inheritance in 2 families. Ten probands were sporadic cases. In the families with AD inheritance, a sex difference was observed between affected and non-affected cases, with an excess of females in the affected group (p < 0.05). In addition to the 78 index cases, 107 new cases were diagnosed. The clinical manifestations of AI observed could be divided into 2 forms, the hypoplastic form in 72% and the hypomineralization form in 28% of the individuals. AD inheritance was seen in 89% of the cases with the hypoplastic form, and in 44% of the cases with the hypomineralization form. In most families with AD or AR inheritance, each family displayed a characteristic manifestation of either hypoplastic or hypomineralization defects. In 3 families, both hypoplastic and hypomineralization forms of AI were seen. In families with X-linked inheritance, the clinical manifestation differed between females and males with males more seriously affected.