ABSTRACTThe literature about the anal sacs of healthy dogs and the pathogenesis, diagnosis and therapy of anal sac impaction and sacculitis are reviewed. Knowledge about the physiological role of the anal sacs is still confusing. The colour and consistency of the anal sac contents are variable in healthy dogs and there are no pathognomonic signs of anal sac impaction or sacculitis. The wide variation in macroscopic detail of anal sac secretions may give rise to misinterpretation and thus overdiagnosis of sacculitis. Other diseases such as vaginitis, flea allergy, atopy, proctitis, parasites and perianal fistulae can lead to similar signs and must be eliminated from the differential diagnosis before the anal sacs are incited as the cause of the signs. Further research is necessary on the morphological, physical and biochemical aspects of the anal sacs and their secretions to define more precise criteria for the diagnosis of impaction and sacculitis. It is imperative that controlled therapeutic trials should be performed, and such studies are indispensable for the rational therapy of anal sac disease.