Varicella, commonly known as chickenpox, is a common viral infection in children. An estimated 3.5 million cases occur annually in the United States. Serious musculoskeletal complications such as osteomyelitis and necrotizing fasciitis, although uncommon, can be life and limb-threatening. The purpose of the current study was to determine the association between varicella and serious musculoskeletal complications necessitating operative treatment and to characterize these infections in otherwise healthy children.We retrospectively reviewed the records of all patients who had been admitted to the Children's Hospital in San Diego because of varicella and its complications during the eleven-year period from 1984 through 1994. All records with an inpatient discharge diagnosis code for varicella were identified.Twenty-seven (6 per cent) of the 417 admissions for varicella were for musculoskeletal complications of the disease necessitating operative treatment. There were seven admissions for osteomyelitis, four for septic arthritis, five for necrotizing fasciitis, ten for a deep-tissue abscess, and one for toxic shock syndrome leading to multiple limb amputations. Seventy-nine (19 per cent) of the 417 admissions occurred in 1994. Eleven (41 per cent) of the twenty-seven musculoskeletal complications that led to operative treatment occurred in 1994, representing a significant increase in the number of such complications compared with the numbers in previous years of the study (p < 0.01).Bacterial pathogens were identified as the cause of twenty-five of the twenty-seven complications that led to operative treatment. Of these twenty-five, twenty-one (84 per cent) were found, on culture, to be caused by group-A ß-hemolytic streptococcus. This pathogen was the cause of the infection in five of the seven patients who had osteomyelitis while Staphylococcus aureus was the cause in only one. Group-A ßhemolytic streptococcus was also the causative organism in two of the four patients who had septic arthritis, three of the five who had necrotizing fasciitis, and all ten who had a deep-tissue abscess. Nine of the eleven musculoskeletal complications leading to operative treatment in 1994 had group-A ß-hemolytic streptococcus as the causative organism.An understanding of the trends of and a high level of suspicion for potentially serious secondary infections in children who have varicella is necessary for prompt recognition and appropriate treatment.