Although neutering of pets is common, recent data show that it might have a significant negative impact on canine health, e.g. by increasing types of various cancers. In spite of a significant increase in knowledge about side effects, the expertise and expectations of veterinarians (V) and dog owners (DO) have to be investigated. To obtain data from V and DO in Scandinavia, 2 separate online questionnaires were used. The results were compared to the litera-ture. A total of 374 V and 3449 DO completed the questionnaires. Neutering was considered to be associated with several positive ef-fects: reduced risk for mammary tumours (♀: V: 93%, DO: 63%) and pseudopregnancy in bitches (♀: DO: 57%), reduced risk for benign prostatic hyperplasia in male dogs (♂: V: 88%, DO: 42%), reduced aggression against other dogs (♂: V: 83%, DO: 60%), reduced urine marking (♂: V: 89%, DO: 61%), reduced tendency for hyperactivity (♂: V: 68%, DO: 51%), for roaming (♂: V: 87%, DO: 64%;♀: V: 64%, DO: 44%), for hypersexuality (♂: V: 95%, DO: 61%; ♀: V: 81%, DO: 40%) and increased life expectancy (♀: V: 45%). Expected negative effects of neutering were increased appetite (♂: V: 91%, DO: 76%; ♀: V: 90%, DO: 76%), increased risk for overweight (♂: DO: 86%, ♀: DO: 84%), for coat changes (♂: V: 84%, DO: 63%; ♀: V: 87%, DO: 65%), urinary incontinence (♀: V: 95%; DO: 36%) and hypothyroid-ism (♂: DO: 27%; ♀: DO: 28%). In conclusion, a certain discrepancy between participants’ expectations and the literature was identified with a tendency to underestimate potential negative effect