Objective: Foodborne disease is a significant global public health concern, with Bacillus cereus being a frequent cause of outbreaks. However, due to the relatively mild symptoms caused by infection with B. cereus, the shorter duration of illness and the challenges of testing for it in both stool and food samples, outbreaks are often underreported. This report describes the epidemiology of cases of foodborne illness, the causative agent and risk factors associated with an outbreak in a boarding school in Seremban district, Negeri Sembilan state, Malaysia, that occurred in November 2021. Methods: Epidemiological, environmental and laboratory investigations were performed. A case was defined as any person with abdominal pain, vomiting or diarrhoea that occurred after consuming food served by the canteen at the school. The data were analysed using Microsoft Excel and the Statistical Package for the Social Sciences (SPSS). Results: A total of 152 cases were identified among the 597 students, giving an attack rate of 25.5%. All cases were females aged 13–17 years. They presented with abdominal pain (100%), nausea (97.4%, 148), vomiting (78.3%, 119) or diarrhoea (61.8%, 94), or a combination of these. The mode of transmission of the outbreak was a continual common source. The foods associated with becoming a case were beef rendang (a dry curry) (odds ratio [OR]: 20.54, 95% CI: 4.89–86.30), rice (OR: 19.62, 95% CI: 2.62–147.01), rice cubes (OR: 18.17, 95% CI: 4.31–76.55) and vermicelli (OR: 17.02, 95% CI: 4.03–71.86). Cross-contamination and inadequate thawing and storage temperatures contributed to the outbreak. Discussion: This outbreak of foodborne illness at a boarding school was likely caused by B. cereus. The findings highlight the importance of proper food preparation, temperature monitoring, hygiene practices among food handlers and compliance with food safety guidelines.