Objective: The aim of the present article is to describe the face and content validity as well as reliability of the Copenhagen Social Relations Questionnaire (CSRQ). Method: The face and content validity test was based on focus group discussions and individual interviews with 31 informants. Another 94 men and women participated in an 8-day test–retest analysis. Results: Informants generally expressed that the questions and response categories were relevant and easy to understand. Themes on structure of social relations, social support, and negative aspects of social relations emerged clearly from the interviews. Two additional themes not covered by CSRQ on dynamics and reciprocity of social relations were identified. Discussion: CSRQ holds satisfactory face and content validity as well as reliability, and is suitable for measuring structure and function of social relations including the negative aspects among middle-aged individuals.