Septic arthritis of hip is a serious problem. Delay in diagnosis and treatment can results in crippling. From September 1983 to May 1993, we have experienced 17 cases of pyogenic arthritis of the hip in neonates and infants. Ten cases were under the age of 1 month old, four were from 1 month to 2 months, and the rest of 3 cases were 11 months old with depicting high incidence in neonates within 1 month. Laboratory findings according to lag periods were as follows; The patients group (n=9) who visited within 3 days after symptom onset manifested high fever (over 38℃) in 2 cases only and 7 cases revealed normal or mild fever. The patients group (n=8) being seen later than 3 days showed high fever in most of cases. Leukocytosis was mostly unspecific in both groups. The average WBC counts tested on admission were 16,052/mm3, ESR 38.3mm/hr,and WBC count dropped to 11,264/mm3, ESR to 27.3 mm/hr after operation. Microbial culture was positive in 10 cases (58.8%), of which 4 were staphylococcus, 5 were streptococcus and 1 was ancinetobacter. Surgical drainage was done through the posterior approach. Long term follow up showed no recurrence and severe complications such as dislocation of head, avascular necrosis and osteomyelitis of proximal femoral metaphysis In conclusion, pyogenic arthritis of hip occurred more common in neonates less than month old and laboratory findings were not always accompanied by fever and hematologic changes especially when the symptom onset was less than 3 days.