Picture fuzzy sets are a direct extension of fuzzy sets and intuitionistic fuzzy sets, recently developed as a mathematical tool for solving uncertainty-related problems. In this paper, a novel similarity measure and corresponding weighted similarity measure between two picture fuzzy sets are proposed after indicating some disadvantages of the current similarity measures of picture fuzzy sets through some exemplary numerical examples. Also, some of their basic properties are discussed. Further, a picture fuzzy decision making algorithm based on the similarity aggregation method is constructed and then applied to the decision making problem. It is also used to deal with a medical diagnosis problem to detect which disease a patient may be suffering from. Finally, the effectiveness of the proposed similarity measure is demonstrated by making comparison with the present picture fuzzy similarity measures.