The authors report their experience with Colloid Cysts of the third ventricle (9 cases treated between 1983 and 1989). Eight of them were punctured using stereotactic approach; five cysts were completely evacuated and the patients are free of recurrence. In three cases, tapping was impossible or the cyst insufficiently evacuated and the patients were secondary operated on (open microsurgical approach). The last case was directly operated on. Colloid cysts cured by stereotactic puncture were all hypo or iso-dense at C.T. scan and had a diameter of more than 1 cm. All these cases have had a M.R.I. exploration and the image of the cyst was always the same increased T1 and T2 signal. Unfortunately, we did not have the opportunity to realize M.R.I. in colloid cysts of a small size and hyperdense at C.T. scan. These results can help to the indication of a stereotactic puncture at the first attempt in some well defined colloid cysts.