In the present paper, the probability for a mesoscale oceanic rings to be seen by a perfect satellite altimeter is investigated. First, the motion of a ring center is determined using a stochastic differential equation. The problem of radar altimeter sampling is then investigated, first in the one-dimensional case, then for two dimensions. The probability of a ring to be seen by a satellite is then computed and is shown to depend on the satellite period and fundamental interval, the mean and standard deviation of the ring speed, and the distance between the ring center and the nearest track when the ring appears. The maximum of this probability and the time at which the maximum arises give an estimate of the satellite ability to sense the rings. The observation of Gulf Stream (GS) warm and cold core rings (WCR/CCR) by the Topex-Poseidon and Geosat altimeters are then presented as examples. For both satellites and ring events, the probability for the ring center to lie on a satellite track (i.e., the entire ring signal is seen) is very low (less than 5%). However, more than 90% of the GS WCRs and 65% of the GS CCRs are seen at least once (i.e., the distance between the ring center and a satellite track is less than the ring radius) with a probability over 80%. The mean probability for the satellite to see a significant part of the ring signal (the distance between the ring center and a satellite track is less than half the ring radius) drops to about 50%. Aliasing between ring motion and satellite sampling should be taken into account during the definition of altimetric data assimilation methods for numerical models. On the other hand, the probability of view is high enough to indicate that altimetric data could improve climatological and statistical studies of mesoscale eddies. ¿ American Geophysical Union 1990