OBJECTIVE: To study the cervical collagen in non-pregnant women with a history of congenital cervical incompetence. SUBJECTS: Ten non-pregnant women with congenital cervical incompetence, defined as cervical incompetence in the first pregnancy in a woman without previous cervical trauma. Seventy-one normal non-pregnant women (31 nulligravidae, nine nulliparous and 31 parous women) served as controls. METHOD: Cervical biopsies were analysed for the hydroxyproline concentration and extractability to express the concentration and the stability of the collagen. RESULTS: Women with cervical incompetence had markedly lower median cervical hydroxyproline concentration when compared to normal parous women (11.1 (range 6.11-18.5) micrograms/mg wet weight vs. 16.9 (range 7.7-29.8) micrograms/mg wet weight; P = 0.003, Mann Whitney test) and the extractability was almost twice the value found in normal parous women (80.2% vs. 49.5%; P = 0.03, Mann Whitney test). Both pregnancy per ce and parturition caused a significant decrease in the hydroxyproline concentration when compared to values found in nulligravidae (P < 0.0001, Kruskall Wallis test). CONCLUSIONS: Congenital cervical incompetence seems associated with a low collagen concentration in the cervical connective tissue in the non-pregnant state.