Avian trichomonosis is a parasitic disease caused by the flagellated protozoan Trichomonas gallinae. Columbiformes are the reservoir host of the parasite, with high levels of infection, but also other domestic and wild birds from a variety of orders are susceptible to the infection and development of gross lesions. A total of 94 clinical cases diagnosed of trichomonosis were selected for the categorization of their lesions at the upper digestive tract. The affected birds were classified into three different categories (mild, moderate and severe) based on the size, the depth and the location of the lesions. Mild grade is found in small and superficial lesions far from the oropharyngeal opening; moderate grade for bigger and deeper lesions, and severe grade for very big and deep lesions that impede swallowing or affect the skull. This revision of lesions will help to understand the pathologic and epidemiological information about avian trichomonosis. Furthermore, it will be helpful for the evaluation, prognosis and possible treatments among veterinarians and related professionals.