Secondary amenorrhoea with elevated gonadotrophins occurring under the age of 40 (premature ovarian failure (POF)), and at the age between 41 and 44 years (early menopause (EM)), respectively, affects 1-2% and 5% of women in the general population. Objective of this study was to evaluate the prevalence of familial cases of POF and EM and to assess the clinical and genetic characteristics of these patients. One hundred and sixty women with idiopathic secondary amenorrhoea before the age of 45 and serum follicle-stimulating hormone (FSH) levels greater than or equal to 40 IU/l were included in the study. Tests performed on patients included complete medical history, pedigree's analysis, clinical pelvic examination, gonadotrophins and thyroid assessment, chromosomal analysis. The 160 patients included in the study showed idiopathic POF (n=130) or EM (n=30). Following pedigree assessment, we were able to identify an incidence of familial cases of 28.5% in the POF group (n=37) and of 50% in the EM group (n=15). POF and EM condition were often present in the same family. There were no differences between POF and EM patients and between familial and sporadic cases regarding age at menarche, personal history, gynaecological history, weight, height and diet habits. There was a statistically significant difference between sporadic and familial cases in age at POF onset: 32.0+/-7.3 years (12-40) compared to 35. 0+/-5.8 (18-40), respectively (P<0.05). The POF and EM families identified showed two or more affected females and transmission through either maternal or paternal relatives; in four families both maternal and paternal transmission was observed. This study suggests that idiopathic POF and EM conditions, differing only in age of menopause onset, may represent a variable expression of the same genetic disease. The different age of menopause onset in these patients may be explained by genetic heterogeneity and/or by different environmental factors. Our results indicate a high rate of familial transmission of the condition. Pedigree's analysis suggests an autosomal or an X-linked dominant sex-limited pattern of inheritance for POF and EM.