Background: Incidences of anorectal malformations (ARM) occur in 1 of 2000e5000 live births and up to 64% have associated malformations (ARMa). The aim of the study was to evaluate possible prenatal risk factors for ARM in a tertiary hospital. Methods: A caseecontrol design was used to compare risk factors in ARM (n Z 44) to a control group (CG; n Z 26). We used modified prenatal questionnaires, analyzed mothers' prenatal records and participants completed a structured interview. Endpoints were medical history, drug consumption, occupational risk factors, and time point of diagnosis, associated malformations and sensitivity of radiological imaging. Results: Our results showed that ARM couples had a significantly higher age difference (p Z 0.028) compared to CG. ARM mothers had more abnormalities during pregnancy (p Z 0.002), more positive vaginal smears of group B streptococci (p Z 0.024), urogenital infections (p Z 0.005), gestosis (p Z 0.03), emesis (p Z 0.025) and higher numbers of chronic diseases (p Z 0.018). ARM mothers took less medication during pregnancy (p Z 0.013) than CG mothers including folic acid (p Z 0.041); their intake of iodine tablets was significantly higher (p Z 0.035) and they continued smoking for longer (p Z 0.036) than CG mothers, and they had more stillbirths (p Z 0.035). In using illegal drug and alcohol use, the groups did not show significant differences. ARMa was present in 68.1% (n Z 30), of which 45.5% were of urogenital origin (n Z 20). ARM diagnosis was made on the first day of life in 72.7% (n Z 32), while diagnosis was delayed in 12 patients (27.3%). Conclusion: A combination of different risk factors seem to be associated with the development of ARM, which takes place at an early stage (<7th week) of pregnancy. Therefore, risk factors influencing fetal development must be critically considered. We advocate an