This is a case study of Feline Hemotropic Mycoplasmosis (previously known as Feline Haemobartonellosis) in a young adult male feline with the sudden onset of signs associated with hemolytic anemia. Feline Hemotropic Mycoplasmosis (or FHM) is a "parasitic" infection of the red blood cells that results in both intravascular and extravascular hemolysis. There are two etiologic agents that infect feline red blood cells: Mycoplasma haemofelis (large form) and Mycoplasma haemominutum (small form). Mycoplasma haemofelis was previously known as the Rickettsial agent Haemobartonella felis. It was recently reclassified due to new information from PCR, Western Blot, and DNA Sequencing tests. Presenting complaint is commonly the sudden onset of behavior changes, lethargy, weakness, and/or pale, icteric mucous membranes. Diagnosis is based on blood smear evaluation. PCR assays are also available. Treatment involves a 3 week course of oral tetracyclines; doxycycline is the drug of choice at 5mg/kg once daily. Glucocorticoids may be administered to reduce extravascular hemolysis. Prognosis of uncomplicated FHM with treatment is excellent although affected cats remain carriers of the organism for life. Concurrent immunosuppression can result in death during the acute phase of the disease or recrudescence of the disease from the carrier state.