Abstract Objectives: It is believed that the age of menarche may be related to polymorphisms in the genes involved in estrogen biosynthesis. A candidate gene is CYP 17 encoding cytochrome P450 c17α, which mediates activity of steroid 17-hydroxylase and 17,20-lyase. A single base-pair change (T→C) in the promoter region of CYP 17 creates a polymorphic variant with an additional SP-1 transcription factor binding site. The aim of our study was to evaluate the relationship between CYP 17 gene polymorphism and the age of menarche. Materials and methods: The study group was composed of 124 healthy Caucasian girls inhabiting the Lublin region (Poland). The observation had began from prepubertal period, thus allowing for the age of menarche to be recorded precisely. CYP 17 polymorphism was assessed with RLFP -PCR using Msp AI restriction endonuclease. An allele with the respective restriction site was designated as A2, whereas one resistant to restriction enzyme as A1. Results: The following frequency of CYP17genotypes has been observed: A1/A1- 36 (29.0%), A1/A2- 67 (54.0%) and A2/A2- 21 (17.0%). The mean age of menarche for these three genotypes did not differ significantly and was: A1/A1- 13.14+/-0.92, A1/A2- 12.93+/-1.04 and A2/A2- 13.40+/-0.91 years, although later age of first menstrual period in carriers of A2/A2 genotype compared with carriers of A1/A2 was nearly statistically significant (p=0.058). The distribution of CYP17genotypes in groups of girls with onset of menarche before and after thirteenth year of age did not differ significantly. Conclusion: The age of menarche in population of Polish girls is not associated with the polymorphism of CYP 17 gene.