Medical social workers may often assess the suicide risk of patients. In addition to their professional assessment via clinical interviews, a valid scale may help provide a quick assessment of the risk of suicide. In Hong Kong, medical social workers wanted to initiate practice-based research with a social work scholar in the university. This research aimed to validate the Hong Kong Chinese version of the Scale for Suicide Ideation (HKC-SSI) and explore its factor structure among patients. Patients who revealed suicidal thoughts to medical social workers or were referred by other health-care professionals for assessing suicidal risks were invited to join this study. They were asked to complete a set of questionnaires which included the HKC-SSI and other scales validating it. The reliability, validity and factor structure of the HKC-SSI were examined. A total of 157 patients completed the questionnaires. The HKC-SSI showed good reliability and demonstrated construct validity by indicating significant correlations with other scales that measure depression, anxiety, presence of meaning and search for meaning in the expected directions. A two-factor structure, ‘motivation’ and ‘preparation’, was found.