A 5-year-old male German shepherd dog was treated with 0.5 mg/ml of vincristine (IV) weekly because of penile transmissible venereal tumour. Three weeks after initial vincristine administration, the dog was admitted to the clinic because of hind limb weakness and regurgitation. Thoracic radiographs revealed the presence of a megaoesophagus. The clinical history of the dog suggested that the egaoesophagus was not present prior to vincristine therapy. Because of an association of megaoesophagus during chemotherapy, it was suggested that the megaoesophagus was related to the vincristine administration. Vincristine withdrawal was followed by a gradual improvement. Both oncologist and chemotherapist should be aware of this complication during chemotherapy. The authors advise recognition of this problem and discontinuation of vincristine, if transient megaoesophagus develops, until symptoms completely disappear

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