OBJECTIVE: Research on social support, attachment insecurity, and negative affect in night eating syndrome (NES) is sparse, although these factors have been proposed as key components of etiological models in other eating disorders. This study investigated whether individuals with night eating (NE) symptoms reported lower social support, greater attachment insecurity, and increased negative affect compared to those without, and examined if negative affect mediated the relationship between interpersonal problems (lack of social support, attachment insecurity) and NE symptoms. METHOD: A representative German population sample of 2423 participants (1297 women, 53.5%) aged between 18 and 92 years completed the Night Eating Questionnaire. Multivariate analysis of variance (MANOVA) analyzed differences between individuals with vs. without NE symptoms in social support, attachment insecurity, and negative affect. Mediation analyses examined cross-sectionally negative affect as a mediator on the relationship between interpersonal problems (lacking social support and attachment insecurity) and NE symptoms. RESULTS: Individuals with NE symptoms reported lower social support (less than small effect), more insecure attachment (small effect), and greater negative affect (small effect) than those without NE symptoms. Negative affect mediated the associations between social support or attachment insecurity and NE symptoms (small effect). All results remained significant after controlling for BMI. DISCUSSION: Given elevated interpersonal problems and negative affect in individuals with vs. without NE symptoms, and the evidence of cross-sectional applicability of the interpersonal model to NES, longitudinal research should examine this mediational effect and investigate interpersonal problems and negative affect as potential risk or maintaining factors of NES.