Background: Peritonitis is the main treatment-related complication of peritoneal dialysis and a primary concern for patients and their relatives. Therefore, understanding their perceptions of peritonitis is important.Objectives: To explore patients' and relatives' perceptions of peritoneal dialysisassociated peritonitis risk, prevention measures and experiences of diagnosis, and experience of perceived stigma.Design: A sequential mixed methods study design was used, including a questionnaire and semi-structured interviews.Participants: Patients using peritoneal dialysis and relatives (n = 75) from six National Health Service organisations from the United Kingdom.Measurements: A structured questionnaire was administered with patients and relatives (n = 75) using peritoneal dialysis; data were analysed using descriptive statistics. Thirty questionnaire respondents were then purposively sampled and interviewed in-depth; data were analysed thematically. Data were collected 2017−2018. Ethical and governance approvals were gained.Results: Qualitative and quantitative analyses were integrated and three themes presented:• Perceptions of risk: participants assessed their risk of developing peritonitis and possible implications on their health and relatives. Participants felt greatly responsible for preventing infection.• Preventing peritonitis: participants reported similar and some differing measures to minimise their risk of developing peritonitis. Participants wanted to be seen as "clean".• Diagnosis of peritonitis: peritonitis diagnosis was embarrassing and stigmatising for many individuals. This was influenced by the response of healthcare professionals and the cause of peritonitis.