In this work we apply Dempster-Shafer's theory of evidence combination for mining medical data. We consider the classification task in two domains: Breast tumors and skin lesions. Classifier outputs are used as a basis for computing beliefs. Dynamic uncertainty assessment is based on class differentiation. We combine the beliefs of three classifiers: k-Nearest Neighbor (kNN), Na?ve Bayesian and Decision Tree. Dempster's rule of combination combines three beliefs to arrive at one final decision. Our experiments with k-fold cross validation show that the nature of the data set has a bigger impact on some classifiers than others and the classification based on combined belief shows better overall accuracy than any individual classifier. We compare the performance of Dempster's combination (with differentiation-based uncertainty assignment) with those of performance-based linear and majority vote combination models. We study the circumstances under which the evidence combination approach improves classification.