An adapter system is provided for adapting and connecting a leadless microstimulator to a separate monopolar, bipolar, or tripolar electrode. Advantageously, the microstimulator does not need to be physically modified. The adapter system encloses the microstimulator and electrically connects the microstimulator to the selected, separate electrode via an extension lead or leads. The adapter has two forms: a monopolar adapter having a single opening or a bipolar adapter having two openings. The separate electrode is equipped with at least one extension lead having a connector that can be inserted into the opening of the monopolar adapter or the bipolar adapter and connect to the microstimulator that is placed within the monopolar or bipolar adapter.