Global data sets of significant wave height (Hs) from altimeter measurements and from the wave model WAM are analyzed statistically to assess the quality of the data. Hs derived from the altimeters aboard Seasat (1978), Geosat (1988), ERS-1 (1993, 1994), and TOPEX (1993, 1994) and from WAM (1988, 1993) and, in addition, from in situ data of Ocean Weather Station M in the North Atlantic are used. First, collocated data sets are compared through linear regression and principal component analysis. From this, a good agreement between Hs of the ERS-1 altimeter (1993) and the WAM model is inferred. Second, the Hs frequency distributions are described by the first four moments. Using the first four moments of linear order statistics, the lognormal and the general extreme value distribution function are found to approximate distributions of Hs best. Hs from Seasat and ERS-1 (1993) deviate from these empirical distribution functions, manifesting weaknesses in the data. Although Hs from ERS-1 have weaknesses, their assimilation into WAM has a positive impact. The assessment of the quality of this existing Hs data provides a prerequisite for the coming assimilation schemes using wave data from synthetic aperture radars and also for climate research studies. ¿ 1998 American Geophysical Union