Gordiid larvae identified as Gordius aquaticus were found encysted on the gut surface of larval lampreys in south Sweden. In the Rorum South River, 89% were infected in June with an average burden of 6.7 larvae/lamprey. Lampetra planeri and L. fluviatilis were equally infected, as were males and females. The incidence declined to 71% in August when it was lowest in L. planeri. The mean burden was 7.6 in L. fluviatilis and 4.3 in L. planeri. In the Stampen Stream where only L. planeri was found, the incidence was 32% in August and mean burden 2.0. Cucullanus truttae was also present. The gordiid is illustrated and briefly described and its life-cycle discussed.