In recommendation systems, items of interest are often classified into categories such as genres of movies. Existing research has shown that diversified recommendations can improve real user experience. However, most existing methods do not consider the fact that users’ levels of interest (i.e., user preferences) in different categories usually vary, and such user preferences are not reflected in the diversified recommendations. We propose an algorithm that considers user preferences for different categories when recommending diversified results, and refer to this problem as personalized recommendation diversification. In the proposed algorithm, a model that captures user preferences for different categories is optimized jointly toward both relevance and diversity. To provide the proposed algorithm with informative training labels and effectively evaluate recommendation diversity, we also propose a new personalized diversity measure. The proposed measure overcomes limitations of existing measures in evaluating recommendation diversity: existing measures either cannot effectively handle user preferences for different categories, or cannot evaluate both relevance and diversity at the same time. Experiments using two real-world datasets confirm the superiority of the proposed algorithm, and show the effectiveness of the proposed measure in capturing user preferences.