To establish the prevalence of numerical and morphological variations of permanent teeth in Swedish 7-year-olds and to accept or reject the hypothesis of a higher prevalence for these conditions in northern Sweden compared to other areas. Cross-sectional. Department of Odontology/Pedodontics, Umeå University, Sweden. A total of 739 healthy Caucasian 7-year-olds residing in the city of Umeå, northern Sweden in 1976. The children were examined clinically and radiographically. The prevalence of hypodontia (excluding third molars) in girls was 8.4%, in boys 6.5%, and in both sexes combined 7.4%. Of the children with hypodontia, the majority (90.9%) lacked one or two teeth. Lower second premolars were the teeth most frequently missing. The prevalence of hyperdontia was 1.9%; 11 girls and three boys were affected; 78% of the supernumerary teeth were mesiodenses. Of the morphological variations, peg-shaped upper lateral incisors were found in 0.8% of the children, double-formation (gemination) in 0.3%, taurodontism in 0.3% and dens invaginatus in 6.8%. One diagnosis was found in 18% of the children, and in almost 8% of them more than one diagnosis was found. The results agree with those obtained in similar populations and are considered representative of this ethnic group. The hypothesis of a genetically determined higher prevalence of numerical and morphological variations in the study population was not verified.