Abstract: The aim of the study was to analyze the polymorphism of cytochrome P450 aromatase gene (CYP19) and the search for the association between the genotypes of two polymorphic sites (CYP19/Cyfr13I and CYP19/PvuII) in the P1.1 promoter region of the CYP19 gene and the age at first calving and calving interval length in Polish Holstein-Friesian cattle. The study used a data set of 909 Polish Holstein-Friesian cows born in the years 1991-1998 and kept in five farms. The analysis of the CYP19 gene polymorphism showed that homozygous AA genotype was most common in both CYP19/Cyfr13I and CYP19/PvuII loci while the least common, also in both loci was the BB genotype. The frequency of the A allele at both loci significantly exceeded the frequency of the B allele. The earliest age at first calving for both CYP19/Cyfr13I and CYP19/PvuII loci demonstrated BB homozygous cows and the latest was found for AA homozygotes. The longest first calving interval was characteristic of cows that were homozygous for the A allele at the CYP19/Cyfr13I locus whereas with respect to the CYP19/PvuII locus, heterozygotes had the longest first calving interval. The shortest first calving interval showed BB homozygotes at both investigated loci. Heterozygotes at the CYP19/Cyfr13I locus had the shortest second calving interval whereas regarding the CYP19/PvuII locus, the shortest second calving interval was found for AA homozygotes.