"Gus", a 5 year old male Boxer dog, presented for evaluation of muscle weakness and regurgitation. On physical examination, Gus was weak, depressed, and in thin body condition. A neurologic examination was consistent with diffuse neuromuscular disease. Initial bloodwork changes were consistent with dehydration, previous corticosteroid administration, and an inflammatory process. Thoracic radiographs revealed a diffuse megaesophagus and aspiration pneumonia, likely secondary to regurgitation. Appropriate differential diagnoses for megaesophagus and diffuse neuromuscular disease were considered. Results from a thyroid panel revealed primary hypothyroidism. An intravenous Tensilon test was positive. Results of acetylcholine receptor antibody titers revealed a strong positive (6.06 nmol/L, normal <0.6 nmol/L), confirming a diagnosis of acquired myasthenia gravis (MG). Gus was administered antibiotics and underwent nebulization and coupage therapy to treat his aspiration pneumonia and was administered anticholinesterase therapy to treat his MG. He responded well to this therapy and was discharged after two weeks of hospitalization.