Abstract Introduction: The etiology of lower-limb neurological deficit after vaginal delivery remains poorly understood. The objective herein was to identify factors associated with this maternal nerve injury after vaginal delivery. Material and methods: A single-center, case–control (matching 1:4) study. Cases were women with a lower-limb neurological deficit that appeared immediately after vaginal delivery. Controls were randomly selected women who gave birth vaginally during the same period, without any deficit. Finally, to assess the rates of factors associated with these deficits, we studied them using a randomly selected 5% sample of the popula- tion with vaginal deliveries. Results: During the 30-month study period, 31 cases were identified among 10 333 women who gave birth vaginally (0.3%, 95% CI 0.20–0.43); 124 controls were also included. After logistic regression, the presence of a neurological deficit after delivery was associated with second-stage labor duration (per hour odds ratio [OR] 3.67, 95% CI 2.09–6.44; OR per standard deviation increase 2.73, 95% CI 1.75–4.25, p < 0.001) and instrumental delivery (OR = 3.24, 95% CI 1.29–8.14, p = 0.012), with no interac- tion effect (p = 0.56). Extrapolation of these factors to a 5% sample of the overall population of women with vaginal births showed that the rate of these deficits would be very low for women with second-stage labor lasting up to 90 min without instru- mental delivery (0.05%) but increased to 1.52% when these factors were combined (OR 33.1, 95% CI 9.4–116.9). Conclusions: Following vaginal delivery, the onset of a neurological deficit is princi- pally associated with the duration of second-stage labor and instrumental delivery. KEYWORDS birth, delivery, lower-limb neurological deficit, maternal nerve injury, second-stage labor, vaginal delivery