In prophylactic treatment of patients having bipolar disorders (BD), lithium, no doubt, plays an important role. The hypothesis of this register study was that said patients, thanks to lithium therapy, would spend fewer and shorter stays in the hospital. We used ipsative control techniques in a study of 60 patients during two periods of 20 months each, one before and the other after the lithium therapy began. We found significant statistical differences regarding the average number (p<.004) and length (p<.001) of stays in hospital comparing pre-lithium treatment to post-lithium treatment. These averages also revealed statistical differences with regard to age (number of stays,p<.002; length of stays,p<.047), with older patients obtaining greater benefit from treatment than younger patients. There were no such differences with regard to gender (number of stays,p<.602; length of stays,p<.584). That BD patients respond favorably to lithium treatment is a well-known finding. On the other hand, we know of no previous study indicating that older patients obtain better results with lithium therapy than do younger patients. Yet because this study occurred over a 20-year period, there are some grounds that probably would substantiate this comparative statement; namely, that one does comply more easily as one gets older, that diagnoses are currently more accurate than they were before, and that care routines have improved.