Data on unrecognized liver cirrhosis in patients with hepatocellular carcinoma (HCC) are derived mainly from cohorts with a risk of selection bias. In a population-based cohort study we aimed to determine the proportion, characteristics, and prognosis of HCC in patients with unrecognized cirrhosis. Using the Swedish quality register for liver cancer and other nationwide registers, we identified all adults with HCC in Sweden between 2012 and 2018 (n = 3,473). The final study cohort comprised 2670 patients with established cirrhosis, of which 1033 (39%) had unrecognized cirrhosis at HCC diagnosis. These patients were more often male, older, and had larger tumors, multinodular cancer, portal vein thrombosis, and extrahepatic metastasis compared to patients with known cirrhosis with HCC and under surveillance (34%). Compared to surveilled patients, those with unrecognized cirrhosis had worse median survival (0.89 years, 95% confidence interval [CI] = 0.78-1.01 vs. 3.79 years, 95%CI = 3.19-4.39), and an adjusted hazard ratio of 2.36 (95%CI = 2.09-2.66). Patients with cirrhosis but not under surveillance (27%) and patients with unrecognized cirrhosis had similar characteristics, such as equal proportions diagnosed at late stage (79%). Cirrhosis is often not recognized in patients with HCC. Unrecognized cirrhosis is associated with more advanced HCC at diagnosis and a worse prognosis. More efforts are needed to diagnose cirrhosis at an earlier stage.