The objective of this study was to identify factors associated with anal sphincter laceration in primiparous women. A subpopulation of 40,923 primiparous women at term with complete data sets was abstracted from a state-wide perinatal database in Germany. Outcome variable was anal sphincter laceration. Independent variables were 17 known obstetrical risk factors/conditions/interventions impacting childbirth recorded on the perinatal data collection sheet. Cross table analysis followed by logistic regression analysis was used for data analysis. Logistic regression showed episiotomy (OR, 3.23; CI, 2.73-3.80) and forceps delivery (OR, 2.68, CI, 2.17-3.33) to be most strongly associated with anal sphincter laceration. Women with a BMI >or= 30 kg/m2, and smokers had a significantly lower risk of anal sphincter laceration. Local, pudendal, and epidural analgesia all reduced the risk of anal sphincter laceration. Iatrogenic factors most strongly associated with anal sphincter laceration in primiparous women include routine episiotomy and forceps delivery.