Joint fluid analysis must be performed as part of the diagnostic workup for acute arthritis, most notably to rule out septic arthritis and to allow the identification of crystal-induced arthritis (gout or calcium pyrophosphate deposition disease), which is one of the most common causes. However, the detection of monosodium urate or calcium pyrophosphate microcrystals is not the only goal of the polarized light microscopy examination of joint fluid. Other, less common microcrystals may be found. Among them are phospholipid microspherules, which are easily recognized microscopically based on their Maltese cross-like appearance. Phospholipid microspherules are a cause of acute arthritis that is often missed by rheumatologists and may therefore be more common than generally believed.