Hepatitis B virus (HBV) is the major cause of hepatocellular carcinoma (HCC) in humans. Domestic cat hepatitis B virus (DCHBV) naturally infects cats worldwide, but the oncogenic potential of this hepadnavirus is unclear. We investigated whether DCHBV contributes to feline HCC. Feline liver biopsies diagnosed with HCC (cases) and lymphocytic cholangitis (controls) were tested for DCHBV DNA by PCR. DCHBV-positive HCCs were further characterised by in situ hybridisation (ISH), whole-genome sequencing (WGS) and phylogenetic analysis. Targeted capture sequencing was used to identify and map viral DNA integrations. DCHBV DNA was detected in 17/71 (23.9 %) HCCs versus 0/88 controls (P