An attachment (24) for a sewing machine (10) to provide simultaneous sewing and sealing of a seam comprises a reel (23) for dispensing a strip of adhesive thermoplastic polymer (25) between fabric members (7,9) to be sewn. A plurality of heated driven rollers (40, 42, 44) opposed to heated idler rollers (50) having a continuous belt (52) thereover collectively exert heat and pressure on the seam, melting the polymer strip (25) so as to seal the seam. Thread (17) having been treated with adhesive thermoplastic polymer may be employed to seal the punctures in the fabric made by the sewing machine's needle (19). The driven rollers are driven in synchronization with the operation of the sewing machine and are engaged with and withdrawn from the seam responsive to operator command.