The purpose of this study was to determine if an association exists between scaphoid-trapezium-trapezoid arthritis and lunate morphology. Plain neutral posteroanterior radiographs were evaluated for 48 patients with STT arthritis and 96 patients from a control group. Lunate type was determined using capitate-triquetrum (C-T) distance. A type I lunate was defined as a C-T distance ĝ‰Currency sign2 mm. A type II lunate was defined as a C-T distance ĝ‰¥4 mm. Lunate type was recorded and compared between those with STT arthritis and a control group. The groups were similar with regard to age, gender and handedness. Type II lunates were found in 83% of cases with STT arthritis and in 64% of controls. STT OA was associated with type II lunate wrists (P = 0.02; OR = 0.35; CI: 0.15-0.82). We postulate that variations in scaphoid motion secondary to lunate morphology may contribute to the development of STT OA.