The aim of this population-based registry study was to explore how cancer influences the health of partners, by examining the onset of new diagnoses for partners, health care use and health care costs among partners living with patients with cancer. The sample consisted of partners of patients with cancer (N = 10 353) and partners of age- and sex-matched controls who did not have cancer (N = 74 592). Diagnoses, health care use and health care costs were studied for a continuous period starting 1 year before the date of cancer diagnosis and continued for 3 years. One year after cancer diagnosis, partners of patients with cancer had significantly more mood disorders, reactions to severe stress and ischaemic heart disease than they exhibited in the year before the diagnosis. Among partners of patients with cancer, the type of cancer was associated with the extent and form of increased health care use and costs; both health care use and costs increased among partners of patients with liver cancer, lung cancer, colon cancer and miscellaneous other cancers. The risk of poorer health varied according to the type of cancer diagnosed, and appeared related to the severity and prognosis of that diagnosis.