Social workers provide services in many cancer settings however there has been limited research into Australian oncology social work practice. This multisite study investigated the reasons those affected by a cancer diagnosis were referred to social workers and the types of intervention undertaken. Clinical data-mining methodology was used to complete a retrospective review of 250 patient medical records. Qualitative and descriptive analyses were undertaken with comparisons to existing classification systems. Findings of significance were that residential location, socio-economic status, gender, relationship status, responsibilities for dependent children, and other complex individual circumstances were key reasons for referral to social workers. Interventions included psychosocial assessment, financial management, counselling, service coordination, and advocacy across multiple systems. Complex circumstances reflecting systemic social inequalities led to higher levels of social worker engagement. The study outcomes indicate that social workers have a significant role in the provision of effective psychosocial cancer care. IMPLICATIONS Poorer cancer outcomes are linked to socio-economic, cultural, and systemic disadvantage, all of which are domains of social work practice. Working across multiple systems, social workers provide a range of skilled interventions to patients, families, carers, and others in complex social situations exacerbated by a diagnosis of cancer. Improving availability and access to social workers will address many of the social circumstances that have a detrimental impact on those affected by cancer.