OBJECTIVE: To study how differences in birth management can influence the frequency and types of perineal lesions. MATERIAL AND METHODS: We compared outcomes and obstetric practices during labour and birth in low-risk primiparous women in two maternity units: one Canadian (maternitA Sainte-Justine, Montreal, Quebec), one French (maternité Cochin-Port-Royal, Paris). We compared the occurrence of perineal lesions--episiotomy and severe perineal tear--in these two maternity units according to delivery method. Furthermore, we studied risk factors for perineal lesions using univariate and multivariate analyses. RESULTS: Among the 1044 births in Montreal and the 1154 births in Paris, the Caesarian-section rate, about 19%, was comparable in both maternity units. Among primiparous women who had a vaginal delivery, the rate of instrumental extraction was higher in the French unit than in the Canadian one (28.2% vs. 21.5%, P < 0.001). The rate of episiotomy was significantly higher in the French unit (65.9%) than in the Canadian one (23.2%), whether the vaginal delivery was spontaneous (OR adjusted = 5.8 [4.4-7.7]) or assisted (OR adjusted = 120.2 [61.0-23.1]). The rate of severe perineal tear was significantly higher in the Canadian maternity unit (11.1%) than in the French one (1.3%), whether the vaginal delivery was spontaneous (OR adjusted = 17.4 [2.4-128.7]) or assisted (OR adjusted = 45.7 [6.1-343.4]). CONCLUSION: The significant differences in episiotomy and severe perineal tear rates observed in low-risk primiparous women are in part due to the different methods used to manage delivery in these two maternity units, particularly with regard to the angle of incision during episiotomy: median in Canada and median-lateral in France.