Aims of this study were to investigate menarcheal age (MA) and menarcheal determinants in 25 girls with cystic fibrosis (CF) and to compare their MA with their respective mothers'. Patients' MA (13.3 +/- 1.1 yr) was on average significantly higher (p<0.0005) than that of the respective mothers (12.2 +/- 1.0 yr) and positively related to it (r=0.055, p<0.005). Six girls experienced menarche after 14.2 yr, ie after the uppest limit of their mothers' MA range. The only parameter which significantly differentiated these 6 patients from the remaining 19 cases was body mass percentile (BMP). Moreover, in the entire patient series a negative correlation was found between MA and BMP. None of the other clinical parameters correlated significantly with MA. No differences in terms of MA were detected in the subgroups of patients with a different glucose tolerance (GT) status and the 12 girls with a pathological GT were not older at menarche than those with normal GT. No correlations were found between either glucose or insulin areas during oral GT test and MA. In the subgroups of patients with a different genotype menarche occurred at a similar age, irrespectively of their genotype. On the basis of our findings we conclude that: a) a menarcheal delay of approximately 1 yr exists between CF girls and their mothers; b) menarcheal delay in CF is not related to either genotype or disease severity or glycometabolic status; c) the only two factors which are able to affect MA in CF are maternal MA and nutritional status.