This article presents the validation study of the Questionnaire of interests for intergenerational practice (QIIP), which aims to contribute to the study of interests on a population level as well as supporting the development and implementation of intergenerational activities and programs through its identification. The design of the study is correlational and cross-generational. The QIIP was applied to 385 residents of Oporto, divided into three age groups. The instrument showed to be valid and revealed good internal consistency concerning the identification of the interests of the sample studied and can be analyzed either by dimension of interest, or by activity item of interest, depending on the goals of intergenerational practices that need to be developed. Upon analysis by dimension and age group, it was found that the Dimension Caring/Protecting and the Dimension Culture refer to common interests, shared among the three age groups. On the other hand, it was observed that the younger group differs from the other age groups in the Dimension Art and in the Dimension "Handiwork", but no significant differences were found in both dimensions between middle-aged adults and older adults. In the Dimension Use of New Technologies, significant differences were registered among all age groups, decreasing in interest as the age increases.