CTX-M-3 has become the most common extended-spectrum beta-lactamase (ESBL) produced by Serratia marcescens in Taiwan. An expanded effort to detect ESBL among 123 nonrepetitive isolates of S. marcescens was made and 15 (12%) ESBL-producers were identified, all revealing CTX-M-3. Without routinely detecting the ESBL for S. marcescens in clinical laboratories, 80% of the ESBL-producers were reported to be susceptible to cefepime. The clinical spectrum of ESBL-producing S. marcescens-related infections included febrile urinary tract infection (n = 3); afebrile pyuria (n = 2); pneumonia (n = 3); spontaneous bacterial peritonitis (n = 3); secondary bacteremia (n = 2) and one each with primary bacteremia and colonization of the central catheter tip. Overall, the 30-day mortality rate was 33.3% (5/15) and the outcome depended on the severity of the underlying disorder and infection per se. In conclusion, although our case numbers were limited, due to the substantial incidence and associated mortality of ESBL-producing S. marcescens and its potential treatment failure by an apparently susceptible cephalosporin, we recommend that the detection and report of ESBL production for S. marcescens in clinical laboratories be made mandatory.