INTRODUCTION: Sarcopenia is a progressive skeletal muscle disorder characterized by a loss of muscle mass, strength, and function. Sarcopenia in acute pancreatitis (AP), a disease with potentially marked catabolism and impaired food intake, could further affect the disease's course and outcome. AIMS: The aim of our study is to determine the prevalence of sarcopenia in patients with AP based on computed tomography (CT) and its association with disease severity and clinical outcomes. PATIENTS AND METHODS: We retrospectively analyzed patients hospitalized for AP in 2020, regardless of etiology. Predictors of disease severity, the APACHE II index, and the BISAP index were determined on admission. To assess pancreatic necrosis and local complications, contrast-enhanced CT of the abdomen with CT Severity Index (CTSI) was performed between days 3 and 5. Assessment of sarcopenia was recorded by determining the psoas muscle index (PMI) and the Hounsfield Unit average calculation (HUAC) at the level of the L3 vertebra. Thresholds for PMI were set at 6.36 cm2/m2 for men and 3.92 cm2/m2 for women, whereas HUAC values were determined at the level of the 25% quartile of values measured in our patients. Local and systemic complications of AP were defined using the revised Atlanta criteria, whereas the impact of comorbidities was assessed by determining the Charlson comorbidity index (CCI). RESULTS: We analyzed 100 patients, of whom 32% were women. The mean age was 67 years (IQR 52-73), and the mean body mass index (BMI) was 27.88 ± 4.72 kg/m2. The mean length of the hospital stay was 11.82 ± 7.68 days. The prevalence of sarcopenia was 16% by PMI and 26% by HUAC. There was no difference in the prevalence of sarcopenia between the sexes. We found significant negative correlations of PMI with APACHE II (r=-0.38; P=0.006), BISAP (r=-0.32; P=0.02), CCI (r=-0.43; P=0.002), and age (r=-0.35; P=0.01) but no significant correlation with CTSI, BMI, and length of hospital stay. HUAC is significantly negatively correlated with APACHE II (r=-0.73; P<0.0001), BISAP (r=-0.58; P<0.0001), BMI (r=-0.39; P=0.005), CCI (r=-0.68; P<0.0001), age (r=-0.58; P<0.0001) and length of hospital stay (r=-0.32; P=0.02) but with no correlation with CTSI. According to the PMI criteria, no significant difference was found between the group of subjects with marked sarcopenia and the group without sarcopenia in all analyzed outcomes. Using HUAC criteria, patients with sarcopenia were significantly older (76±7.23 vs 59.22±14.12; P=0.0001) and had significantly higher BMI (30.85±3.77 vs 26.84±4.62; P=0.007). The same group had significantly higher values of APACHE II (10.92±20.74 vs 6.32±8.28; P=0.0001) and CCI index (5±2.48 vs 2.19±1.81; P=0.0001). No differences were observed in other outcomes. Mortality analysis was not possible because no deaths occurred. CONCLUSION: Sarcopenia is quite common in patients with AP already on admission. As expected, sarcopenia in this group is also associated with older age and more concomitant diseases, but it also seems to be associated with higher BMI values. There are indications that sarcopenia is associated with potentially more severe forms of the disease, but this has not been confirmed in terms of the frequency of specific clinical outcomes. This is likely a consequence of the relatively small number of patients studied with a rather limited number of observed complications and a very low proportion of patients with a severe AP. Further studies in a larger number of subjects with a higher proportion of severe forms of AP are needed for more reliable results.