To determine frequency of Pseudomonas aeruginosa producing classic and extended spectrum beta-lactamases in neonatology service reservoirs at Regional Hospital of Cajamarca, between november 2005 and february 2006, samples were obtained using cotton buds from sinks, water taps, incubators, cradles, etc. that were in the service. Cetrimide agar, Gram coloration, oxidase and citrate tests were used for isolation and identification of P. aeruginosa. Yodometric method was used for determination of classic beta-lactamases and synergy with double disk to detect extended spectrum beta-lactamases. From 97 samples 20 P. aeruginosa isolations were obtained (21%); of these 45% (9/20) were producing of classic beta-lactamases, that were found in reservoirs of common use as sinks and water taps, only 10% (2/20) were producers of extended spectrum beta-lactamases. In valued neonatology service there is risk of infections for P. aeruginosa producing classic and extended spectrum beta-lactamases. .