We have measured the microhardness of various amorphous hydrogenated carbon thin films that were grown on both the anode and the cathode of our plasma deposition system. We observe no difference in microhardness between films with the same optical bandgap, whether grown on the cathode or on the anode. We conclude that the ion bombardment during cathode growth does not contribute to the hardness of the films. In contrast, we observe a large variation in microhardness as a function of optical bandgap. We conclude that it is increasing hydrogen concentration, found primarily in the clusters and not in the crosslinks, that decreases the hardness of our films. Finally, we observe that the addition of nitrogen to our films does not change the microhardness; again, the hardness is primarily determined by the hydrogen concentration.