53-year-old female with follicular grade 3 lymphoma with clear marrow involvement (a). This patient had bilateral iliac marrow biopsy. The post-treatment PET-CT (b) shows diffuse uniform increase in marrow uptake. However, the SUV actually decreases (from 6.7 to 4.9) on the right iliac bone marrow with pathologic confirmation of marrow involvement (b). On the contrary, the SUV over the pathologically negative left iliac bone marrow increases (from 2.7 to 4.2) due to normal hematopoietic response.