Recently, the survival rates of extremely low-birth-weight (ELBW) infants have improved with the development of neonatal intensive care. However, these infants were susceptible to intestinal perforation due to prematurity, fluid restriction, and injection of indomethacin, etc. Because of the risks of transportation, anesthesia and surgery itself, peritoneal drainage has been compared with laparotomy. Through our experience, we investigate the usefulness of peritoneal drainage retrospectively. From 1997 to 2007, six ELBW (M:F=5:1) underwent primary peritoneal drainage for intestinal perforation. Their median birth weight was 685g (405~870) and gestational age was $25^{+1}$ weeks ($24^{+3}{sim}27^{+0}$). We noticed the intestinal perforation at median 10.5 days (8~18) after birth, and placed Penrose drain or Jackson-Pratt drain through right lower quadrant incision under local anesthesia. The cause of intestinal perforation was necrotizing enterocolitis in one patient, but that of the others was not clear. Three patients who showed normal platelet count and stable vital signs recovered uneventfully. Two patients (birth weight less than 500g) who showed unstable vital signs and low platelet count (12,000 / $mm^3$ to 30,000 / $mm^3$)expired despite aggressive resuscitation. One patient required laparotomy due to persistent intestinal obstruction after drain removal and survived. Our experience shows that peritoneal drainage was an acceptable treatment for ELBW infants and the prognosis was related to vital sign and platelet count at the time of intestinal perforation, and birth weight.