Aim Perforated appendicitis has poorer clinical outcomes compared to non‐perforated appendicitis. However, accurate outcome comparisons in research and clinical audits are challenged by its wide spectrum of manifestation. Previous attempts at the classification of severity have been complex and difficult to reproduce. In our study, we used another institution's (Jones et al., TX, USA) previously described simple classification system of peritoneal contamination and examined its usefulness in predicting outcomes. Methods With ethical approval, we retrospectively reviewed the records of all paediatric patients operated at our institution for perforated appendicitis from 2016 to 2017. Patient demographics, intra‐operative and histological findings, post‐operative outcomes and length of stay were collected. Patients were categorised into group 1 (purulence in right lower quadrant only) and group 2 (contamination in two or more quadrants). Post‐operative complications were defined as procedure‐related (e.g. post‐operative ileus, intra‐abdominal abscess, visceral injury) and non‐procedure‐related (e.g. bronchospasm). Statistical analysis using χ2 tests for categorical data and Mann–Whitney U‐tests for non‐parametric continuous variables was performed, with a significance of P < 0.05. Results There were 134 eligible patients. We excluded 19 with incomplete data, leaving 115 for analysis, of which 69 (60%) were in group 2. Those in group 2 had a longer stay (P = 0.005) and more post‐operative complications (P = 0.001), particularly procedure‐related events (P = 0.006). There were no differences in age (P = 0.182), gender (P = 0.876), readmission rate (P = 0.317) and non‐procedure‐related post‐operative complications (0.152). Conclusion This simple classification of perforated appendicitis appears to differentiate clinical outcomes well, particularly for iatrogenic morbidity, making it useful for operative preparation and outcomes research.