Felty syndrome is a potentially serious condition associated with seropositive rheumatoid arthritis. It is characterized by rheumatoid arthritis along with splenomegaly and granulocytopenia.

Felty syndrome is closely associated with rheumatoid arthritis, which affects about 1% of the general population. Of this 1%, Felty syndrome develops in about 1% to 3%. Therefore the estimated frequency is about 0.01% to 0.03% of the general population. Women are affected at a 3:1 ratio compared to men. It affects Caucasians more than any other race.

The pathophysiologic origin of Felty syndrome is not fully understood. Granulocytes coated with immune complexes, diminished granulocyte growth factor levels, and circulating autoantibodies have been demonstrated, as well as linkages to a human leukocyte antigen genotype, suggesting a genetic contribution to development of the disorder.