Phosphodiesterase 11 (PDE11) is the latest isoform of the phosphodiesterase family to be identified. Interest in PDE11 has increased recently because tadalafil, an oral phosphodiesterase 5 inhibitor, cross reacts with PDE11. The function of PDE11 remains largely unknown, but growing evidence points to a possible role in male reproduction. The published literature on PDE11 structure, function and expression is reviewed.