The aim of this study was to determine the prevalence of hypodontia, hyperodontia, and double formation of primary teeth in Icelandic children in the dental stage DS 02 (primary dentition complete). The study group comprised 927 children (498 boys and 429 girls). This was about 9% of all children aged 0-83 months in Reykjavik at the time of the registration of these anomalies, during the winter of 1978-1979. The children included those presenting for regular examinations in two health centers, children from three kindergartens, and seven pre-school classes from two schools in Reykjavik. Of these children 61.9% were selected for this study as they proved to be in dental stage DS 02 (primary teeth fully erupted). The prevalences were hypodontia, 0.5%; hyperodontia, 0.5%; and double formation, 0.7%. Comparison was made with earlier results from Iceland and with results from several other nations.