Subperiosteal abscesses (SAs) are a complication of osteomyelitis that requires surgical intervention. This study aimed to characterize the occurrence of subsequent complications in pediatric patients with osteomyelitis and accompanying SA. Fourteen pediatric patients with SAs were included. We recorded clinical information, including age at diagnosis, interval (days) between the onset of symptoms and diagnosis, location of SAs (long/flat bone), pathogens [methicillin-resistant Staphylococcus aureus (MRSA)/non-MRSA], treatment period (days) and any subsequent complications. Patients were classified based on SAs with or without complications. Mann-Whitney U and Fisher exact tests were used for statistical analyses, and data are expressed as median and interquartile range. Six patients (42.9%) had subsequent complications. There were significant differences in location of SAs between these two groups (long/flat bone, with versus without complication = 6/0 versus 3/5; P = 0.031). No significant differences were observed between the groups in terms of age [with versus without complication = 13.8 (9.7-24.5) versus 556.3 (5.0-107.8) months; P = 0.491], the interval (days) between symptoms onset and diagnosis [with versus without complications = 5 (1-10) versus 5 (3-6.5) days; P = 0.950], pathogenesis (MRSA/non-MRSA, with versus without complication = 4/2 versus 2/6; P = 0.277) and treatment period [with versus without complication = 50.5 (31-57) versus 29 (24.5-41.5) days; P = 0.108]. Pediatric patients with SAs in the long bones have a higher likelihood of experiencing subsequent complications than those with SAs in flat bones. Physicians should carefully manage this vulnerable patient group.