Objectives: Postneonatal infant deaths are mainly associated with environmental and socioeconomic causes that are preventable. The aim of this study was to identify the sociodemographic risk factors for postneonatal infant death. Methods: This is a case–control study. The case group consisted of mothers residing in Bursa who lost their babies in the postneonatal period (n=113). The control group included mothers living in Bursa whose children were of age 12–24 months. The control group received health services from the same family physician as the case group and gave birth in the same month. No sample was selected from the case group, and all data were collected by a questionnaire using the face-to-face technique. Results: This case–control study was conducted with 101 (34.1%) cases and 195 (65.9%) controls. The analyses of the model, which included all variables significant in binary analyses, showed that the infant mortality rate was higher in those residing in Bursa for less than 10 years (OR=4.211, 95%CI=2.202–8.023, p=0.001); was higher in those who were related to their spouses (OR=2.232, 95%CI=1.112–4.632, p=0.001); was higher in those who had 3 or more pregnancies (OR=3.814, 95%CI=2.001–7.275, p=0.001); was higher in male babies (OR=2.201, 95%CI=1.204–4.001, p=0.001), and was higher in those with a birth weight of ≤2.500 g (OR=6.881, 95%CI=2.811–16.901, p=0.001). Conclusion: The medical history of the patients should be evaluated, and the patients with high risk should follow more closely and frequently to reduce postneonatal infant mortality.