Introduction: Cholecystitis is a medical condition characterized by the inflamation of gallbladder. In over 90% of cases, acute cholecystitis develops due to a gallstone obstructing the cystic duct. Understanding modifiable risk factors, such as obesity, is critical for developing effective prevention and management strategies. Aim: To study the association between Body Mass Index (BMI) and acute and chronic cholecystitis. Materials and Methods: This retrospective observational study was conducted out at Prince Abdulaziz Bin Musaad Hospital in Arar City, Saudi Arabia, between January 2024 and December 2024, involving 320 adult patients. Demographic data were collected from the medical records and BMI was calculated. Frequencies and percentages were utilised for gender and diagnosis, while the mean +/- standard deviation were calculated for age and BMI. A chi-square test was applied to evaluate the association between the variables, with a significance level of <0.05 considered significant. Results: Of the 320 patients, 228 (71.2%) were females. Of these, 167 (52.2%) patients were diagnosed with chronic cholecystitis, while 153 (47.8%) were diagnosed with acute cholecystitis. Only 52 patients (16.3% of the total) had an ideal BMI. The data were divided into two BMI groups: BMI <30 kg/m(2) and BMI >30 kg/m(2). A significant difference (p-value=0.042) was observed, with a higher proportion of acute cholecystitis cases in the BMI <30 kg/m(2) group. Conclusion: There was a higher incidence of acute cholecystitis in patients with a BMI below 30 compared to those with a BMI above 30, indicating that BMI may influence the type of cholecystitis.