BACKGROUND: Chronic hepatitis B virus (HBV) infection is the predominant cause of hepatocellular carcinoma in west Africa, yet data on the incidence of HBV-related hepatocellular carcinoma remain scarce. We aimed to describe the uptake and early outcomes of systematic ultrasound-based hepatocellular carcinoma screening in SEN-B, which is a prospective HBV cohort in Senegal. METHODS: In this prospective cohort study, we included treatment-naive, HBsAg-positive individuals who were referred to the two infectious diseases clinics (the Department of Tropical and Infectious Diseases and Ambulatory Treatment Center) at Fann University Hospital of Dakar, Senegal, between Oct 1, 2019, and Oct 31, 2022. All participants resided within the Dakar region. Participants underwent abdominal ultrasound, transient elastography, and clinical and virological assessments at inclusion and every 6 months. Liver lesions at least 1 cm in diameter on ultrasound were assessed using four-phase CT, MRI, or liver biopsy. Adherence to hepatocellular carcinoma surveillance was measured using the proportion of time covered, calculated by dividing the cumulative months covered by abdominal ultrasound examinations by the overall follow-up time, defined as the number of months from the date of cohort entry until the last recorded visit, hepatocellular carcinoma diagnosis, or death. Optimal adherence was defined as a proportion of time covered of 100%. FINDINGS: Overall, 755 (99·6%) of 758 participants had at least one abdominal ultrasound performed. The median age of the enrolled participants was 31 years (IQR 25-39), 355 (47·0%) of 755 participants were women, and 82 (10·9%) had a family history of hepatocellular carcinoma. 15 (2·0%) of 755 individuals were HBeAg positive, 206 (27·3%) of 755 individuals had HBV DNA of more than 2000 IU/mL, and 27 (3·6%) of 755 had elastography-defined liver cirrhosis. Of ten (1·3%) participants with a focal lesion at least 1 cm at initial assessment, CT or MRI ruled out hepatocellular carcinoma in nine, whereas imaging and subsequent liver biopsy confirmed one patient with hepatocellular carcinoma. Two further patients with hepatocellular carcinoma were diagnosed at study presentation due to the presence of portal thrombosis on ultrasound. Excluding the three participants with hepatocellular carcinoma identified at baseline, 752 participants were eligible for screening every 6 months. Median follow-up time was 12 months (IQR 6-18) and the median number of ultrasounds per patient was 3 (2-4). During 809·5 person-years of follow-up, one incident hepatocellular carcinoma was reported, resulting in an incidence rate of 1·24 cases per 1000 person-years (95% CI 0·18-8·80). Overall, 702 (93·0%) of 755 participants showed optimal hepatocellular carcinoma surveillance, but this proportion decreased to 77·8% (42 of 54 participants) after 24 months. INTERPRETATION: Hepatocellular carcinoma screening is feasible in HBV research cohorts in west Africa, but its longer-term acceptability needs to be evaluated. Long-term hepatocellular carcinoma incidence data are crucial for shaping tailored screening recommendations. FUNDING: Swiss National Science Foundation, the Swiss Cancer Research Foundation, the National Cancer Institute, and Roche Diagnostics. TRANSLATION: For the French translation of the abstract see Supplementary Materials section.