Systemic mastocytosis (SM) is a rare clonal disorder of mast cells that can range from chronic smouldering type to aggressive mast cell leukaemia. It presents with non-specific symptoms like urticaria pigmentosa, unexplained flushing, hypotension and abdominal cramps, which may lead to a misdiagnosis, if there is no high index of clinical suspicion. This is a case report of a 52-year-old lady, with systemic mastocytosis, who presented with severe chronic back ache and no other clinical features. X – ray revealed lytic lesions in the lumbar vertebrae and bone marrow aspiration and a trephine biopsy examination showed infiltration by mast cells, with a positivity for Toluidine blue stain and CD 117. She was also noted to have peripheral eosinophilia, which is frequently encountered with this condition. She was diagnosed to have chronic indolent systemic mastocytosis which involved the bone predominantly.