A patient with primary hyperparathyroidism and known pseudogout presented with an acute flare of the right knee. Gram stain was negative, and many intracellular calcium pyrophosphate dihydrate (CPPD) crystals were seen by both compensated polarized light and transmission electron microscopy. Cultures grew Staphylococcus aureus; the joint was probably seeded by an antecedent skin infection, with enzymatic "strip mining" precipitating acute pseudogout. The patient was refractory to therapy with oxacillin, naproxen, intravenous colchicine, and closed drainage. Arthroscopic debridement with insertion of drainage tubes led to rapid improvement, and offers an alternative to arthrotomy in septic knee arthritis unresponsive to closed drainage.