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A histopathological survey of commercial farms in Ecuador culturing redclaw crayfish, Cherax quadricarinatus (Von Martens), revealed the presence of different viral, bacterial and non-infectious pathologies. A total of 536 animals from 27 different farms were analysed during a 3-year period; 25, 154 and 357 specimens in 1995, 1996 and 1997, respectively. From the total sampled, a virus referred to as Cherax quadricarinatus bacilliform virus (CqBV) had a prevalence of 44% in animals examined during 1996 and 33% in 1997. A rickettsia-like organism (RLO) was detected in five specimens sampled from three different farms in 1995. This RLO was detected in 36 and 12% of samples analysed in 1996 and 1997, respectively, and was the infectious agent most frequently associated with mortalities above 60%. Co-infection by CqBV and the RLO was observed in 18 and 3% of the crayfish examined in 1997 and 1998, respectively. Five specimens out of 25 examined presented no sign of an infectious agent during 1995. The proportion of specimens testing negative by histopathology to known or suspected infectious agents was 25 and 32% in 1996 and 1997, respectively. Although different infectious agents were present in cultured crayfish, farms in general had overall survivals higher than 50% in most ponds. Other conditions observed included an intracellular prokaryotic organism, iron granules in the R and F cells of the hepatopancreas, different species of epibionts on the surface of the gills and body, and two cases of haemocytic enteritis. Two cases of serious mortality in different farms were associated with the presence of Cowdry type A inclusions, pyknosis, karyorrhexis and haemocytic infiltration in the stomach hypodermis and the antennal gland.