The number of reported cases of rib osteomyelitis is very infrequent. Magnetic resonance is generally the best test in these cases, due to its high sensitivity and specificity. However, given this technique has some drawbacks, it is usually restricted to cases of bad evolution. A relevant, easy to perform, bedside imaging test is the point of care ultrasound. We present the case of a 2-month-old infant with a rib osteomyelitis detected by point-of-care ultrasound in the context of sepsis after abdominal surgery. The thoracic ultrasound revealed a lesion adjacent to the right sixth rib and round extra-parenchymal collection in the right costophrenic sinus. Chest computed tomography confirmed the presence of a hypodense collection at the costochondral junction of the right seventh rib with pleural thickening and an increase in soft tissues, compatible with osteomyelitis. Our ultrasound finding in the absence of specific clinical data of rib osteomyelitis led us to a change in the duration of the antibiotic treatment already established and therefore likely led to an improvement in the patient’s prognosis. The ultrasound has gained increasing prominence due to its usefulness in diagnosis and monitoring, especially in pediatric intensive care, given the ease of use at the patient’s bedside.