Background: Canine leishmaniosis (CanL) is a common infectious disease. Age, sex and breed might influence the type of clinical and pathological manifestations that dogs develop. The main objective of this retrospective cross-sectional study was to determine if an association between age, sex, breed and size and the clinical findings of CanL exists. Material and methods: Dogs with a diagnosis of leishmaniosis were enrolled (n = 123). Clinical information, including signalment, clinical signs and laboratory abnormalities, was retrieved from medical records from different veterinary facilities from Catalonia. Results: Young dogs developed less frequently systemic signs (p = 0.0046), renal (p = 0.0019) and haematologic (p = 0.0275) abnormalities, while dermatologic signs were more common in young and adult dogs compared with old ones (p = 0.0451). Young dogs showed proteinuria less often than adult and old dogs (p = 0.0029). Young dogs did not present renal azotemia, while old dogs showed occasionally renal azotemia (p = 0.0478). Young dogs were mainly classified as mild-moderate LeishVet clinical stages of the disease, and very rarely as severe-very severe LeishVet clinical stages, compared with adult and old dogs (p = 0.0457). Purebred dogs significantly developed ulcerative dermatitis more frequently than crossbred dogs (p = 0.0460). Conclusion: This study describes that age is associated with differences in clinicopathological findings of CanL.