Introduction: Polymorphism of the gene encoding α-1 chain of type I collagen (COL1A1) may influence the mechanical properties of the pelvic floor connective tissue. Aim of study: We examined possible role of G→T substitution in transcription factor Sp1 binding site in the gene encoding α-1 chain of type I collagen (COL1A1) in the development of pelvic organ prolapse. Materials and methods: The study group consisted of 37 women with pelvic floor defects graded according POPQ scale as stage II, III and IV. All study group patients underwent reconstructive surgery of the pelvic floor. We enrolled forty control subjects. All of them were treated for benign gynecological conditions other then stress urinary incontinence or pelvic organ prolapse. DNA was obtained from peripheral blood leukocytes. The fragment of the first intron of COL1A1 gene containing Sp1 binding site was amplified by PCR and analysis of restriction fragment length polymorphism was done. Results: The GG polymorphism in COL1A1 gene was identified in 26 (70.3%), GT sequence in 10 (27%) and TT in 1 (2.7%) patient. The distribution of the investigated polymorphisms in the control group were: 27 (67.5%), 9 (22.5%) and 4 (10%), respectively. We do not found association between investigated polymorphic variants and pelvic organ prolapse (chi2 test, p=ns). Conclusion: G→T substitution in transcription factor Sp1 binding site in the COLIA1 gene does not increase the risk of development of pelvic floor defect (POPQ stages II, III, IV).