The Atlantic cod (Gadus morhua) and other Gadidae species are sound producing fish species. Both female and male cod produce a characteristic low frequency grunt which is easily recognizable from other species. However, only males produce this sound during the spawning season. Recent studies on the Atlantic cod have shown that passive acoustic monitoring (PAM) offers an additional perspective for monitoring the occurrence, spatial extent and duration of spawning cod aggregations. Since cod is by far the most economically important fish in Iceland a great effort has been set on studying various aspects of this species. The PAM method has been used in Icelandic waters for the last five years, primarily for monitoring cetacean species. Additionally, an extensive collection of cod and other fish sound has been gathered on these recordings. A preliminary study conducted in Skjálfandi bay, NE-Iceland, using two PAM recorders, has shown diel and seasonal differences in acoustic activity of the Atlantic cod during the winter. Significant relationship was found between acoustic activity and environmental parameters. The recording locations were separated by 13 km but the results showed synchronized sound behavior throughout the winter at these two locations. These preliminary findings indicate the usability of acoustic monitoring of the cod in Icelandic waters.