Anguillicoloides crassus infection in wild European eels (Anguilla anguilla) from Mar Menor, a hypersaline coastal lagoon situated on the shores of the Mediterranean in south-east Spain, was evaluated. As well, an artificial digestion is described for the detection, isolation and counting of larval stages in the swimbladder wall. A total of 109 eels were collected between November 2008 and March 2009 and adult worms were recovered from the swimbladders of infected eels. The detected prevalence was 7.34%. Second-stage larvae (L2) numbers ranged from one to thousands per swimbladder. This developmental stage was the most prevalent parasite stage detected in infected eels. L2 were even found in eels harbouring neither pre-adult nor adult nematodes, which could indicate that infected eels are chronically infected. The lack of a suitable intermediate host for this nematode or the recent introduction of A. crassus into this environment could be the causes of the low prevalence of this parasite in eels from Mar Menor lagoon.