We present a new method of combining satellite altimetry and tide gauge data to obtain improved estimates of absolute (or geocentric) vertical crustal motion at tide gauges within a semi-enclosed sea. As an illustration, we combine TOPEX/POSEIDON altimetry data (1992--2001) and 25 long-term (>40 years) tide gauge records around the Baltic Sea region of Fennoscandia, an area where crustal deformation is dominated by glacial isostatic adjustment (GIA). A comparison of the estimated vertical motion, at 1--11 mm/yr, with independent solutions from 10 collocated BIFROST GPS sites, shows a difference of 0.2 ¿ 0.9 mm/yr, thus verifying the accuracy and robustness of the procedure. The solution uncertainty is estimated at 0.4 mm/yr, which is significantly lower than previous analyses of this type. We conclude that our technique can potentially provide accurate vertical motion observations globally where long-term tide gauge records exist.