Background: Mental health and social professionals are at high risk of experiencing at least one patient suicide during their career. Aims: This paper investigates the impact of patient suicide on the reactions and working practices of mental health and social professionals. It also examines how such an impact may vary depending on the professionals’ characteristics, their relationship with the patient, as well as the institutional setting in which they work. Methods: 275 professionals working in sociomedical institutions in French-speaking Switzerland completed a questionnaire. Results: Patient suicide can cause a wide range of long-lasting reactions and changes in the working practices of mental health and social professionals. Professional’s gender, place of suicide, as well as responsibility for and emotional attachment to the patient significantly influence the impact that a patient suicide has on such professionals. Professional’s age, the type of profession, the number of suicides experienced, and previous suicide attempts by the deceased patient were also found to play a significant role with regard to changes in working practices. Conclusions: Beyond the emotional and professional impact, patient suicide may have also a formative influence, encouraging professionals to review and improve their working practices. Recommendations to help mental health and social professionals who have experienced a patient suicide are discussed.