OBJECTIVE Cancer is a global public health issue that continues to increase because of aging and adoption of cancer-causing behaviours. In Ethiopia, cancer belongs to the second most common non-communicable disease. Cancer patients face a range of unmet needs in multiple aspects of their lives. Supportive care is defined as essential care that helps patients to cope with cancer. This study aims to assess the predictors of unmet supportive care needs in adult cancer patients in Ethiopia. METHODS Institution-based cross-sectional study was done from February to March 2019 in adult cancer patients. Three hundred seventy-one patients were interviewed using convenience sampling. Supportive care needs were used as outcome variables, dichotomized as 'no need' and 'unmet needs'. Variables with a p-value of <0.2 were candidates for multivariable logistic regression. RESULTS From 371 patients, 69.8% were females with a mean age of 47 years; the commonest type of cancer was gynaecological cancer. Information about diagnosis, stage of cancer, time since diagnosis, age, wealth index, employment status, gender, type of treatment, history of recurrence, type of cancer and information about diagnosis modified by the source of information were predictors of unmet supportive care needs. CONCLUSIONS The study emphasised the importance of considering sociodemographic, clinical and information-related factors when dealing with cancer patients. Programmes, guidelines and services that focus on supportive care needs should be established and/or implemented.