Background: The choice of activities responding to the needs of people with moderate to severe dementia is a growing concern for care providers trying to target the need for a feeling of self-accomplishment by adapting activities to the abilities of elderly patients. The activities created by Maria Montessori seem to be adaptable to this clientele. This study evaluates the short-term effects, as compared to regular activities offered in the milieu. Methods: This is a quasi-experimental study where each of the 14 participants was observed and filmed in two conditions: during Montessori activities, during regular activities, and one control condition (no activity). Results: The results show that Montessori activities have a significant effect on affect and on participation in the activity. They support the hypothesis that when activities correspond to the needs and abilities of a person with dementia, these positive effects are also observed on behaviours. Conclusions: This study enabled its authors to corroborate the findings presented in the literature and to contribute additional elements on the positive effects of the use of Montessori activities and philosophy. Used with people with moderate to severe dementia these allow the satisfaction of their basic psychological needs, their well being, and hence, on their quality of life. (Contains 2 tables.)