The organization Hearing Dogs for Deaf People provides assistance dogs that alert their deaf or hard-of-hearing recipients to key sounds, thus increasing their independence and also providing companionship. Fifty-one recipients took part in a longitudinal study to monitor the dogs' working performance over time and to examine the social and psychological effects of having a Hearing Dog. The Profile of Mood State (POMS) questionnaire and the General Health Questionnaire (GHQ) were used together with a Hearing Dog Questionnaire (HDQ) specifically developed for this study. There were a number of significant differences in measures of well-being between the period prior to placing the Hearing Dog and the period after placement, but there were no comparable differences during the year-long waiting period prior to placement of the dog. Recipients reported significant reductions in hearing-related problems such as response to environmental sounds; significant reductions in measures of tension, anxiety, and depression; and significant improvements in social involvement and independence. The longitudinal nature of this study supports evidence that these improvements persist for some time after the placement of a dog, with significant differences being reported, in many cases, up to 18 months after acquiring a dog.