Context Animal-assisted interventions have been used in recent years to complement other therapies of various types for dementia patients. Objective The study intended to evaluate the benefits of dog-assisted interventions for the emotional, behavioral, cognitive, and functional areas of the lives of dementia patients. Design The research team designed an experimental study that used dog-assisted therapy (DAT) as the intervention. Setting The study was conducted at the Enoc Center, a nursing home, in Azucaica, Toledo, Spain. Participants Participants were 21 residents who had been living at the center for more than one year, were over 65 years old, and had symptoms associated with dementia or affective disorders. Intervention Participants were randomly divided into three groups: the control, intervention, and healthy groups. The intervention and healthy groups attended the DAT in addition to the center's regular therapies. The control group didn't attend the DAT but did attend the center's regular therapies. The program occurred over six months, with weekly sessions of 45 minutes in both cases. Outcome measures Participants were evaluated at baseline and postintervention using specific scales appropriate to an area: (1) cognitive-Mini-Mental Status Examination (MMSE), (2) functional-Modified Barthel Index, (3) affective-Yesavage Geriatric Depression Scale: Short Form and (4) behavioral-Neuropsychiatric Inventory Scale (NPI). Results The study revealed significant differences between the control group and the intervention group and between the control group and the healthy group in the cognitive, affective, and behavioral areas but not in the functional area. Conclusions The program was beneficial for elderly institutionalized patients with dementia in the emotional, behavioral, and cognitive areas.