Bacterial pyoderma is common in small animal practice. Usually there is an associated underlying disease, but little is known about the prevalence of underlying diseases in dogs with recurrent pyoderma. The aim of this study was to analyse the frequency of the different underlying diseases in dogs with recurrent pyoderma. In total, 157 animals with recurrent pyoderma were identified in hospital records from 2008 to 2013 and the data analysed for primary diseases. The time between recurrences, the type of clinical signs and the age at pyoderma onset were also evaluated. At least one primary disease was found in 107 dogs. Allergies were the primary cause in 63 dogs, environmental allergy was the most frequent (n=45) and was often associated with other allergies, followed by hypothyroidism (n=12) and hyperadrenocorticism (n=6). Sixteen dogs with recurrent pyoderma suffered from demodicosis. In young dogs with recurrent pyoderma an allergy work-up combined with deep skin scrapings should lead to a diagnosis of the underlying disease in most of the cases. In dogs in which pyoderma began in middle or old age, hormonal testing and ruling out a possible flea infestation should be the first steps.