We describe a case of 47-year-old woman affected by human epidermal growth factor receptor-2-positive breast cancer with a diffuse leptomeningeal carcinomatosis. An intense uptake of F-choline was reported at fused PET/MRI images in the brain, compatible with a diffuse leptomeningeal disease. This case highlights that F-choline PET would be used for the identification of leptomeningeal involvement in patients affected by breast cancer, as a support of MRI images.