This letter describes an algorithm development for the production of a large-scale fully polarimetric synthetic aperture radar (SAR) (PolSAR) mosaic using multitemporal Advanced Land Observing Satellite Phased Array type L-band SAR acquisitions. The PolSAR data were collected during the snow-melting season in 2007 over Finnish Lapland, resulting in considerable radiometric differences between mosaiced scenes originating at different dates. Several variants of polarimetric seam hiding between the original PolSAR images were proposed and evaluated in order to effectively eliminate stripes in the mosaic. The impact of such seam-hiding procedure on PolSAR classification performance was studied, along with the technical aspects of producing the PolSAR mosaic. The obtained results indicate the advantages of the considered seam-hiding procedures for producing homogeneous mosaics and obtaining consistent classification results in a single classification step.