This study is based upon a written survey of keepers of neutered dogs about the behaviour of 209 male and 382 female dogs. The main findings are: Male dogs show behavioural changes after castration more often and more distinctly than female dogs after neutering. Behavioural problems in most cases are reduced or have even disappeared after neutering (male dogs 74%, female dogs 59%). At best, hypersexuality and connected problems are changed as expected. 49 of 80 aggressive male dogs and 25 of 47 female dogs are more gentle after neutering. 10 bitches appeared to be aggressive only after being neutered. Particularly feeding behaviour changes in 42% of the male dogs and 32% of the female dogs towards an increased intake of food, which also leads to an increase in body weight. This corresponds to decreasing activity, which is indicated by increasing time of rest (male dogs 36%, female dogs 18%) and decreasing motivation to move. Motivation for playing, watchfulness and perseverance change more seldomly and sometimes increase. The character of the neutered animals is predominantly described as "devoted, friendly and kind". Changes of behaviour following neutering depend on many influencing factors. Above all effective obedience training, but also the family situation of the owner, time factors, conditions of keeping and contact with other dogs have different impacts on the control of the individual behavioural problems.