OBJECTIVE This was to review the literature published, to point out shortcomings and to suggest areas in need of improvement concerning the diagnosis and prevalence of MIH. METHODS A broad search of the PubMed database was conducted. Relevant papers published in English were identified after a review of their titles, abstracts or full reading of the papers. Papers were selected if the number of children with at least one first permanent molar affected by demarcated opacities could be deciphered. Targeted publications were critically assessed by the author concerning examination criteria, selection and character of the study groups, examiners' calibration and result presentation. RESULTS The initial search revealed 414 papers of which 24 met the inclusion criteria. A wide variation in defect prevalence (2.4 - 40.2 %) was reported. Cross comparison of the results of the various studies were difficult because of use of different indices and criteria, examination variability, methods of recording and different age groups. CONCLUSIONS Further standardization of study design and methods is needed to make the results comparable.