BACKGROUND: The optimal treatment remains controversial for acute left-sided colon perforation. Therefore, the effectiveness and safety of primary anastomosis versus Hartmann's operation (HP) was compared in a case-matched control study. METHODS: Thirty consecutive patients with primary anastomosis and protective ileostomy (PAS) were matched to 30 HP patients, controlling for age, gender, American Society of Anesthesiologists (ASA) score, body mass index (BMI), and peritonitis severity (Hinchey). In a second analysis, PAS patients with purulent peritonitis (Hinchey 3) were matched to patients with primary anastomosis without ileostomy (PA). RESULTS: Hospital mortality was similar between HP (17%) and PAS (10%). Complication frequency and severity (requiring re-intervention or admission to the Intensive Care Unit [ICU]) were comparable for the first operation (60% versus 56% and 30% versus 32%). The stoma reversal rate was higher in PAS than in HP (96% versus 60%, p = 0.001), with significantly fewer complications (23% versus 66%, p = 0.02), and lower severity (7% versus 33%, p = 0.02). Additional analysis of PAS versus PA showed similar morbidity (52% versus 41%, p = 0.45) and complication severity (18% versus 24%, p = 0.51), whereas overall operation time and hospital stay were significantly shorter in PA (169 versus 320 min, p = 0.003, 17 versus 28 days, p < 0.001). CONCLUSIONS: Primary anastomosis and protective ileostomy is a superior treatment to HP in acute left-sided colon perforation. In the absence of feculent peritonitis an ileostomy appears unnecessary.