Informal payments for health care are a well-known phenomenon in many health care systems around the world. While informal payments could be an important source of health care financing, they have an adverse impact on efficiency and access to care, and are a major impediment to ongoing health care reforms. This paper aims to study the scale and patterns of informal patient payments for out-patient and in-patient services in three former-socialist countries: Bulgaria, Hungary and Ukraine. The data are collected in 2010 and 2011 based on national representative samples and are analysed in pooled models to explain variations in payments. The results of the cross-country comparison suggest a relatively higher prevalence of informal patient payments in Ukraine and Hungary than in Bulgaria, where patients also have to pay formal user charges in the public sector. Nevertheless, informal payments for hospitalization in Bulgaria are quite extensive. We observe some differences in informal payments across the years. Variations in payment size are mainly explained by the nature, type and need for services, fee awareness and, on some occasions, by household income. Interpreted within the context of structural differences (e.g. reform paths, regulations, funding, user fees, anti-corruption policies), the findings of our study have implications on how to address informal payments for health care.