Lack of social contacts has been associated with an increased risk of cancer mortality, but it is not known whether living alone increases the risk of cancer incidence or case fatality. We examined the association between living alone with cancer incidence, case-fatality and all-cause mortality in eight most common cancers. All patients with their first cancer diagnosis in 2000–2017 were identified from the nationwide Finnish Cancer Registry. Information on living arrangements was derived from Statistics Finland. The incidence analyses were conducted using Poisson regression. The total Finnish population served as the population at risk. Fine-Gray model was used to estimate case-fatality and Cox proportional regression model all-cause mortality. In men, we found an association between history of living alone and excess lung cancer incidence but living alone seemed to be associated with lower incidence of prostate cancer and skin melanoma. In women, living alone was more consistently associated with higher incidence of all studied cancers. Cancer patients living alone had an 11%–80% statistically significantly increased case-fatality and all-cause mortality in all studied cancers in men and in breast, colorectal and lung cancer in women. Living alone is consistently associated with increased cancer incidence risk in women but only in some cancers in men. Both men and women living alone had an increased risk of all-cause mortality after cancer diagnosis.