In this study, histopathological characterization after surgical removal of the injection site masses in dogs was performed. Twelve dogs (11 males and 1 female), mainly Labrador retrievers (n = 8), 5 to 40 month old, stemming from the same dog farm have exhibited injection site masses 75 days after miscellaneous subcutaneous injections for cough treatment. All masses were removed with radical surgical resection under general anaesthesia and no radiotherapy or chemotherapy was performed. By conventional histopathological analysis with haematoxylin-eosin, Masson's trichrome and Alcian blue staining, and immunohistochemistry using anti-vimentine or anti-alpha smooth muscle actin as primary antibodies, chronic inflammatory granulomas were identified in the majority of cases (6/12) but fibrosarcoma (characterized by spindle shaped well-differentiated vimentine positive neoplastic fibrocytes associated with giant cells) was diagnosed in 4 cases and fibromyxosarcoma and haemangiopericytoma (with vimentine and alpha-smooth muscle actin positive fibrocytes) were also identified in the 2 other cases. No local recurrence or metastasis was observed in any case. It was concluded that among soft tissue sarcomas which occurred at the injection site, fibrosarcoma was the most common in dogs but this tumour type was less aggressive in dogs than in cats.