Osteomyelitis is an uncommon infection that is considered to be a childhood disease. Diagnosis is frequently delayed, as it is a very rare condition and also because of its variable presentation. After an accurate diagnosis and treatment, the outcome is favorable in children. We present one case without recent previous infection, antecedent trauma, or penetrating injury, illustrating the difficulties in diagnosis. Nontraumatic osteomyelitis of the patella should be regarded as a rare hematogenous infection. A high index of suspicion should be addressed for early recognition. Study design is level of evidence: level IV.