Background: Consanguineous marriage is a common practice in Turkey. Sociodemographic and cultural factors associated with it are still unclear.

Aim: The purpose of this study was to investigate the association between sociodemographic and fertility factors and consanguineous marriages in an urban slum of a metropolitan area in Turkey.

Methods: This community-based case-control study was conducted in Bayrakli Municipality health centres. Of the 1243 married women, 85 consanguineously married were included in the case group. A control group in non-consanguineous marriages consisted of 85 women matched to cases according to age and neighbourhood. Information about the subjects’ sociodemographic features, fertility history and opinions about consanguineous marriage was collected.

Results: Factors that were associated with consanguinity included; having a low level of education (OR = 2.7, CI = 1.1–6.7), a brief duration time in Izmir after migration (OR = 4.7, CI = 1.9–11.6) and consanguineous parents (OR = 3.8, CI = 1.5–9.7). Despite the increased numbers in fertility features and higher perinatal mortality for first cousin marriages, there was no significant difference in the mean numbers of pregnancies, births, stillbirths and living children.

Conclusion: Time after migration and educational background of women were the main factors associated with consanguineous marriages. Public health interventions to reduce consanguineous marriage in urban areas should target socioeconomically disadvantaged populations in cities.