A 67-year-old man developed Serratia marcescens peritonitis within a week of commencing peritoneal dialysis. Dialysate cultures isolated multidrug-resistant S. marcescens, which was treated with intraperitoneal meropenem. This unusual case highlights the problem of multidrug-resistant peritoneal dialysis infections and the potential viability of intraperitoneal meropenem as ambulatory peritonitis therapy.