Animal-assisted interventions (AAIs) are co-therapies in which the animal is an integral and active part of the treatment process. Dogs are widely involved in AAI projects, but little data are available to determine if AAI sessions are a source of stress for the dogs. Understanding the emotional state of animals and highlighting any signal of stress is crucial maintaining the wellness of the animals and in enhancing the probability of success of the AAI. The purpose of this study is to assess if dogs present signs of stress during animal assisted therapies sessions. The sample consisted of nine dogs, belonging to the members of the A.N.U.C.S.S. (the National Association for the Use of Dogs for Social Aims) association. Dogs lived with their owners and their health was checked by a vet once a week. Patients involved in the AAI project had disabilities due to mental disorder and/or psychomotor problems. During the therapeutic sessions, patients had to guide the dog along facilitated agility routes and/or perform the activities of cuddling and brushing the dog. When a dog accomplished a task, the patient gave him/her a reward (throwing a ball or a biscuit). Dogs were observed for a total of 174 h, 47 h before, 81 h during, and 46 h after AAI sessions. Each session of observation lasted 10-30 min. The differences of behavioural patterns in the three contexts were analysed by mean of the non-parametric Friedman test. Dogs never showed aggressive and stereotyped behaviour; the level of anxious behaviour was low and similar in all three kinds of sessions. During therapeutic sessions, attention, affiliative behavioural patterns, and sniffing behaviour increased. The highest level of attention of dogs was directed toward their conductor, rather than to the patient and to the other operator present. The results suggest that the amount of work dogs went through was adequate and that dogs did not show behavioural signs of stress.