The goal of this US study was to determine the frequency of horizontal violence in a perinatal service and its effect on patient outcomes. A 24-question survey instrument was completed online by 63 nurses. The results indicated that labour and delivery wards experience a higher frequency of horizontal violence than other units in the perinatal service. They also showed that the mother and baby unit demonstrates a higher frequency of recipient or victim behaviours. A relationship between horizontal violence and ineffective communication, as well as a relationship between horizontal violence and poor patient outcomes or near misses, was demonstrated.