This report details the investigation of renal disease associated with neurologic signs and deaths in a captive research colony of the endangered swift parrot (Lathamus discolor). The syndrome affected birds irregularly during 11 months from October 1999 to September 2000. Ten birds from 4 aviaries were clinically affected, and 9 birds died. The most common clinical signs were weight loss, neurologic dysfunction (ataxia and generalized tremors), and articular gout. At necropsy, common findings included gross nephropathy, visceral gout, and gonadal regression or inflammation. Histopathologic changes included renal tubular degeneration and accumulations of black crystals, assumed to be urates, in renal tubules and collecting ducts. These histopathologic changes are nonspecific and could be associated with a wide variety of nephrotoxins including, but not limited to, heavy metals, organic solvents, phenol, antibacterial agents, pesticides, and ethylene glycol. The syndrome was associated with the feeding of a high-protein diet and the presence of nesting boxes and other environmental factors. A number of potentially toxic substances were found in the swift parrots' environment, including nitrate fertilizer, zinc from galvanized wire, and potentially toxic wood fragments (Tasmanian sassafras [Atherosperma moschatum]). However, not all affected birds were exposed to these toxins, or diagnostic testing ruled them out of consideration. Regardless of the initial cause of renal damage, the overall renal pathologic changes were consistent with a urate nephropathy. There is still uncertainty as to the initial cause of the neurologic disease and renal damage despite the intensive investigation described here. The immediate deterioration of 2 swift parrots after the reintroduction of the high-protein diet led us to suspect that dietary levels of protein might be a contributing factor to the renal disease.