A 63-year old man developed acute monoarthritis in the dorsum of the left foot. Polarized light microscopy of the synovial fluid from his third metatarsophalangeal joint revealed numerous positively birefringent lipid spherules with a maltese cross appearance. Positively birefringent lipid spherules can be found in association with acute, otherwise unexplained arthritis, and may induce synovial inflammation similar to that seen in other types of crystal-induced arthritis. We report a case of acute monoarthritis in which large numbers of positively birefringent lipid spherules were present in a hyperlipidemic diabetic patient.