OBJECTIVESAcute osteomyelitis is a challenging diagnosis to make in the pediatric emergency department (ED), in part because of variability in its presentation. There are limited data detailing the presenting features of pediatric osteomyelitis, factors that are essential to understand to inform diagnostic decision making. We sought to describe relevant clinical data that contributed to the diagnosis of acute osteomyelitis in children presenting to a pediatric ED. METHODSThis was a 10-year retrospective cohort study of patients 18 years or younger diagnosed with acute osteomyelitis in the ED of a large tertiary care childrenʼs hospital. Collected data included demographics, clinical history, patient-reported symptoms, vital signs, physical examination findings, and results of basic laboratory, microbiologic, and imaging studies. Descriptive statistics were used to summarize key findings. RESULTSTwo hundred eleven cases of acute osteomyelitis were identified during the study period. The median age was 8.4 years, with 61.1% male. One hundred twenty-seven patients (60.2%) presented to care more than once before being diagnosed. Common symptoms included pain (94.3%), functional limitation (83.9%), and fever (76.3%). Common examination findings included functional limitation (78.2%), focal tenderness (73.5%), and swelling (52.1%). One hundred seventeen patients (55.5%) were febrile during their ED evaluation. Elevated C-reactive protein (>0.8 mg/dL, 92.9%) and erythrocyte sedimentation rate (>10 mm/h, 94.3%) were the most sensitive laboratory markers. CONCLUSIONSFever may be absent in up to a quarter of pediatric patients with acute osteomyelitis. Although highly sensitive, inflammatory marker elevations were more modest than those reported previously in cases of pediatric septic arthritis.