A 38-year-old man experienced an intermittent low-grade fever with generalized eruption, followed by rapidly progressive right hemiplegia. Neuroimaging revealed a ring-like enhanced mass in the left premotor cortex surrounded by marked perifocal edema. The syphilitic titer was high both in the serum and in the cerebrospinal fluid. Open biopsy of the lesion revealed the tumor consisted of inflammatory cells associated with plasmacyte infiltration to the perivascular region as well as to the dura, which is consistent with the definition of syphilitic gumma. The abnormalities in neurology and in neuroimaging improved dramatically after antisyphilitic treatment. Difficulties in differentiating a cerebral gumma from other diseases are discussed.