AIM: According to the literature, the scientific evidence is insufficient to answer the question as to whether premature birth causes altered tooth-crown dimensions. The aim of this study was to evaluate permanent tooth-crown dimensions in prematurely born children and to compare the findings with full-term born controls. SUBJECTS AND METHOD: White pre-term children, 8 to 10 years of age, were selected from the Swedish Medical Birth Register. One group consisted of 36 extremely pre-term children (born before the 29th gestational week), and the other 37 very pre-term children (born during gestational weeks 29 to 32). The pre-term children were compared with a control group of 41 full-term children, who were matched for gender, age, nationality and living area. Clinical examinations were undertaken and study casts and panoramic radiographs were obtained for each child. The permanent maxillary and mandibular first molars, central incisors and laterals were measured with a digital sliding calliper on the study casts. The tooth-crowns were measured both mesiodistally and buccolingually. The examiner conducting the measurement analysis was unaware of the subject grouping. RESULTS: The maxillary and mandibular first molars were smaller mesiodistally and buccolingually (P ≤ 0.01) whereas the central incisors and lower laterals were smaller mesiodistally (P ≤ 0.02) in the extremely pre-term group compared with the full-term group. A reduction in tooth size of 5-8 per cent was found between the extremely pre-term group and the full-term group. Furthermore, the maxillary first molars and mandibular left first molar were also smaller mesiodistally (P ≤ 0.035) in the extremely pre-term group compared with the very pre-term group. CONCLUSION: Premature birth is associated with reduced toothcrown dimensions of the permanent teeth, and the more preterm the birth the smaller the tooth-crown dimensions.