ABSTRACTObjectives. To define the presence of lung metastasis in bitches with malignant mammary neoplasms. Material and methods. Thirty female dogs that were attended at Veterinary Hospital (University of Antioquia, Medellin, Colombia) were selected for the study. At consultation clinical variables and grade of mammary and inguinal lymph node compromise were registered. Latero-lateral and ventral-dorsal radiographic images of thorax were done for identification of radiographic lesions suggestive of lung metastasis. At surgery biopsies of affected mammary glands were taken for histopathological study and classification of tumors. Data were analyzed by descriptive statistics. Results. The average (± standard error) age at clinical diagnosis was 10.87±2.65 year old. French poodle (46.6%) cross-breed (13.3%) and Schnauzer (10%) were the breeds most frequently affected by mammary tumors. The most frequent tumor found was carcinoma (81%), followed by adenoma (8.1%), and other types (10.8%). The most frequently affected mammary glands by tumors were the right and the left inguinal glands (70% and 66.6%, respectively). Five out of 30 bitches (16.6%) had lung metastasis according to radiographic examination. From this group of dogs, 4 out of 5 neoplasms (80%) were diagnosed as complex carcinoma by histopathology diagnosis. Conclusions. We provide evidence suggesting that complex carcinoma is the most frequent mammary tumor in bitches in our city and it is highly related to lung metastasis..