Neonatal septic arthritis of the knee was encountered in nine infants during a two-year period, representing an incidence of 16.5 per 1,000 admissions to a neonatal intensive care unit. The etiologic agents included Staphylococcus aureus (3), Klebsiella (1), Streptococcus, group B (2), and Candida albicans (3). Two infants with systemic fungal infection died. Arthritis was the presenting feature of neonatal septicemia in three of six infants with bacterial infection and was accompanied by osteomyelitis in two. In eight of the infants, the same organism was cultured from the skin of the umbilicus as was cultured from the joint. Umbilical catheters had been placed in all of these infants. Full recovery of joint function has been noted in the seven surviving infants.