This study aimed to establish the prevalence of psychiatric morbidity among cancer patients' caregivers and to identify markers of risk. Using the Psychiatric Assessment Schedule (a standardized psychiatric interview), the authors assessed 222 caregivers retrospectively. Thirty-one caregivers (14%) had developed an affective disorder during the two years since the patients' initial cancer diagnoses. Caregivers who were the patient's partner were more likely to develop anxiety, depression, or both when their ill spouse had developed these symptoms. Notably, the prevalence of affective disorders among female caregivers was comparable to the prevalence among patients (23%). Female nonpartner caregivers developed disorders as frequently as partners did. Female caregivers with a prior history of affective disorder who reported more illness-related concerns appeared to be at particular risk, providing useful markers for clinical practice.