Macroscopic thromboembolic disease has been associated with canine neoplasia, whereas prevalence studies of concurrent microthrombi and tumour-cell emboli are lacking. This retrospective study investigated microthrombi and tumour cell emboli by reviewing pathology records of dogs diagnosed with lymphoma, sarcoma, carcinoma and mast cell tumours with a concurrent description of thrombi or emboli. Pathology reports and medical records of cases with either tumour biopsies and/or post mortems with a diagnosis of neoplasia were reviewed for the presence of microthrombi, macrothrombi and/or tumour-cell emboli and the association with tumour type. Of the 28 895 canine cases in the database, 21 252 (73.5%) were antemortem biopsy specimens and 7643 were post mortems (26.5%); 2274 solid tumours were identified, 2107 (92.7%) were antemortem biopsy diagnoses and 167 (7.3%) were post mortem diagnoses. The prevalence of solid tumour types in the database (28 895 cases) was 872 (3.0%) lymphoma, 722 (2.5%) sarcoma, 455 (1.6%) carcinoma and 225 (0.8%) mast cell tumour. The prevalence of microthrombi associated with these tumours was 58/2274 (2.6%). Intra-tumoral microthrombi were reported in 53/2274 (2.3%) cases, the majority in sarcomas (37/53, 69.8%). No macrothrombi were reported. Tumour-cell emboli were identified in 39/2274 (1.7%) cases, 31/39 (79.5%) were extra-tumoral or distant emboli, and carcinoma the most commonly associated tumour (29/39; 74.4%). Microthrombi were reported in 2.6% of cases, the majority in sarcomas and tumour-cell emboli were identified in 1.7% of cases, the majority carcinomas. Prospective investigations are necessary to explore the potential clinical and prognostic implications of microthrombi and tumour-cell emboli in canine neoplasia.