<b><i>Background:</i></b> Previous studies have suggested body composition as a predictor of sorafenib toxicity and outcome in patients with advanced hepatocellular carcinoma (HCC). Large studies on the impact of body composition parameters in European HCC patients are lacking. Our aim was to validate the prognostic value of body composition parameters in Dutch patients with HCC treated with sorafenib. <b><i>Patients and Methods:</i></b> A retrospective analysis was performed in a cohort of HCC patients treated with sorafenib at two Dutch tertiary referral centers between 2007 and 2016. Body composition (adipose and skeletal muscle tissue) was measured at baseline by computed tomography (CT). Low skeletal muscle mass (SMM) and density were defined using published cut-offs. Body composition parameters were correlated with overall survival (OS), time to progression, response rate, and toxicity. <b><i>Results:</i></b> A total of 278 patients were included, mostly Child-Pugh class A (85%) and Barcelona Clinic Liver Cancer (BCLC) stage C (73%), with a median OS of 9.5 months (95% CI 8.1–11.0). Patients with combined low SMM and low total adipose tissue index (TATI) (<i>n</i> = 68, 25%) had a poor median OS (5.8, 95% CI 4.8–6.8) compared with other patients (11.7, 95% CI 9.4–14.0). Combined low SMM and low TATI remained an independent predictor of OS (HR 1.56, 95% CI 1.15–2.11, <i>p</i> = 0.004) after adjusting for known prognostic factors. There was no association between body composition and sorafenib toxicity. <b><i>Conclusions:</i></b> In Dutch HCC patients treated with sorafenib, the combined presence of low SMM and low TATI was associated with impaired survival, independent of known prognostic factors. CT assessment of body composition may provide additional prognostic information prior to sorafenib treatment.