The unprecedented accuracy of TOPEX/POSEIDON (T/P) altimeter data warrants a new evaluation of the methods typically used to form time series of sea level change. Whereas explicit removal of orbit error has always been required as a first step in altimeter data processing, the T/P analysis presented here is based simply on unadjusted, monthly averages. This approach has the advantage of retaining the large-scale ocean signal, which would be distorted by orbit adjustment. Using 16 months of data, we have evaluated the T/P monthly means on spatial scales ranging from mesoscale to global. In the tropical Pacific, comparisons with 17 island tide gauge records and dynamic height derived from 36 thermistor moorings show that the altimeter data have an accuracy of approximately 2 cm when averaged over spatial scales of a few hundred kilometers. On basin scales in the northern hemisphere, similar agreement is found between the T/P data and the dynamic height climatology of Levitus (1982). These new altimeter observations are thus providing the first reliable view of global sea level changes on seasonal-to-interannual timescales. ¿ American Geophysical Union 1994