This paper investigates the association between advanced maternal age and under-5 mortality and morbidity in Turkey, and is the first such study in the country to use a sibling comparison model to analyze this phenomenon. The study is based on data obtained from the 2013 Turkey Demographic and Health Survey, and analyzes the association of advanced maternal age with: (1) under-five mortality, using Cox proportional hazard models and their stratified versions to compare sibling groups born to the same mother in the 1978-2013 period, and (2) under-five morbidity; specifically, being born with low birth weight, stunting, underweight, and wasting based on between- and within-sibling groups models for the 2008-2013 period. Overall, our findings suggest that the hazard of under-5 mortality increases as maternal age increases. We conclude that period effects have failed to reverse the impeding effects of advanced maternal age on child mortality. Between-sibling group models indicate a positive but close to null association between advanced maternal age and child morbidity in general, although these positive associations vanish once we apply within-sibling group models. This result can be partially attributed to our controlling for unobserved characteristics specific to sibling groups, in addition to other methodological differences.