Escherichia coli is commonly found in outbreaks of diarrhoea in mink during the production season although its role as a primary causal organism remains unclear. The present study was undertaken to determine the serogroups and antimicrobial susceptibility of E. coli isolates from healthy and diarrhoeic mink. Rectal swabs were taken from healthy and diseased animals, on six different farms, once at the onset of disease and again approximately 2 weeks later. The swabs were subjected to bacteriological investigation; a total of 210 E. coli were isolated, 98 from healthy animals and 112 from diseased. All isolates were serotyped and MICs were determined for nine antimicrobial compounds. Non-haemolytic isolates numbered 147, whereas 63 were haemolytic. Both haemolytic and non-haemolytic isolates were isolated from both healthy and diseased animals. A wide range of serogroups was detected, the most frequent being O2 (11.0%), O78 (11.0%), O153 (7.1%), O25 (5.7%), O6 (4.8%), and O15 (4.8%), but diarrhoea was not associated with specific serogroups. All isolates were sensitive to enrofloxacin, neomycin, gentamicin and colistin. In contrast, considerable variations in susceptibility were found among the six mink farms, for tetracycline (0–46.4%, average 21.9), ampicillin (2.9–50.0%, average 23.3), spectinomycin (8.0–35.7%, average 21.9), sulfamethoxazole (8.6–57.7%, average 30.0) and trimethoprim (0–35.7%, average 9.5). Resistance to tetracycline was statistically more prevalent among haemolytic than among non-haemolytic strains. In conclusion, serogrouping and haemolysin testing failed to identify any association with diarrhoeal disease and antimicrobial resistance was highly variable between different mink farms.