Background :     Pyrexia of unknown origin (PUO) is a diagnostic problem in clinical practice, while diagnosis may remain obscure for several weeks. The role of bone marrow examination is crucial in the diagnostic approach.

Method :–  Total 110 patients having PUO were examined. Their bone marrow aspiration by Salah needle and biopsy by 11G trephine biopsy needle was performed.

Result :–     A definitive diagnosis could be achieved in 92 (84%) Patients. Fifty six patients had infectious etiology with tuberculosis being the commonest cause of PUO.

Conclusion :–      Bone Marrow examination showed a good diagnostic yield in evaluation of pyrexia of unknown origin.