Crop acariasis was diagnosed in two green-winged macaws (Ara chloropterus) by crop biopsy (Case 1) or postmortem (Case 2). Case 1 was a 3-yr-old macaw of unknown gender that presented with vomiting and crop and proventricular dilatation. Crop biopsies were obtained and submitted for histopathology to screen for ganglioneuritis/proventricular dilatation disease (PDD). After a diagnosis of mild lymphoplasmacytic inflammation presumably involving a nervous ganglion, three additional recuts of the four fragments of crop biopsy tissue processed revealed moderate chronic multifocal granulomatous serositis with intralesional and perilesional encapsulated mites. In these recuts, lymphoplasmacytic ganglioneuritis was confirmed. This macaw was treated with ivermectin, and clinical signs resolved. Case 2 was a female presented for necropsy with a clinical suspicion of PDD, which was confirmed by histopathology (ganglioneuritis, leiomiositis, encephalitis, chromaffin adrenalitis). Concurrent diseases included severe biventricular dilated cardiomyopathy, severe fungal necrotizing pneumonia with fungal thromboembolism and crop acariasis. Mites were embedded in the serosa, which had fibrosis; inflammation in the crop was more intense around mites and included macrophages in these areas. Despite the ability of diverse mites to parasitize internal organs such as the trachea, pericardium, or subcutis in birds, crop acariasis has apparently been not reported in macaws or any other avian species. The findings in Case 1 indicate that crop acariasis should be included in the differential diagnosis of PDD-like disease in macaws. Recovery after treatment with ivermectin suggests acariasis may have caused or contributed to the clinical presentation in this animal. Interestingly, the other affected macaw, Case 2, died of PDD.