Background: Pyomyositis is an uncommon bacterial infection of the skeletal muscle withformation of an intramuscular abscess. The common muscles involved are the pelvic and thigh muscles. We are reporting a case of pyomyositis of the right teres minor muscle with abscess formation secondary to methicillin resistant staphylococcus aureus (MRSA) bacteraemia in a three month old infant with an excellent outcome. Case presentation: A previously healthy baby girl presented with high fever for 2 days.Examination was normal except for subtle reduction of movement of the right upper limb (RUL). Initial blood tests showed evidence of a bacterial infection with a high C reactive protein. Intravenous cefotaxime was commenced after blood culture. Lumbar puncture became positive while blood culture grew MRSA and ultrasonography of right shoulder joint was normal. The paucity of RUL movements became more pronounced. Repeated careful examination revealed a slightly swollen tender point just beneath the right shoulder joint suggestive of an abscess. Focussed ultrasonography revealed an abscess within right teres minor muscle. Urgent surgery performed with pus culture revealing MRSA. Fever settled overnight, paucity of movement of the right upper arm improved dramatically with complete recovery following treatment. Conclusion: Pyomyositis is a rare clinical entity in paediatrics. It could present at an age as early as three months. In addition, this infant had involvement of rotator cuff muscles, not previously reported. Therefore, if a young infant presents with fever, paucity of movement of a limb, high inflammatory markers pyomyositis is worth considering in the differential diagnoses.