Purpose: Amongst children with complex appendicitis (CA), post-operative intra-abdominal abscesses (IAA) occur in approximately 18% of cases (1). Peritoneal lavage (PL) is widely used with the expectation that it reduces complications, despite limited supporting evidence. We hypothesised that suction only (SO) without irrigation would be non-inferior to PL in children with CA. Methodology: We conducted a randomised controlled trial (RCT) including three centres, comparing PL and SO in children undergoing laparoscopic appendicectomy for CA. Recruitment occurred from April 2020 to January 2025, but was interrupted during the COVID-19 pandemic. The sequentially numbered, opaque, sealed envelopes (SNOSE) method was used for randomisation. The PL group underwent irrigation with >2000mls 0.9% saline. In the SO <100mls was used. Outcomes included IAA, WI, small bowel obstruction (SBO) and length of stay (LoS). Standardised site-based data collection was performed. Results: In total 195 participants were recruited, including 111 in the PL group and 84 in the SO group. There were no significant demographic differences. Average LoS was 6.5/7 in the PL group and 5.5/7 in the SO group, p<0.01. In the PL group there were 14 IAA detected, compared to 8 in the SO group (P=0.7). Both groups only had one participant that developed a WI (p=1.0), and 2 participants that developed SBO, p=1.0. Conclusion: Our RCT found that PL in children with CA was associated with a statistically significant, although minimal increase in LoS. However, incidence of complicating IAA, WI and SBO were the same amongst PL and SO groups. This supports the hypothesis of non-inferiority of SO compared to PL. Reference: 1. Peter SDS, Sharp SW, Holcomb GW, Ostlie DJ. An evidence-based definition for perforated appendicitis derived from a prospective randomized trial. J Pediatr Surg. 2008;43(12):2242-5. children. J Pediatr Surg. 2012;47(2):317-21.