Indoor radon was systematically surveyed in the town of Niksic-the second largest town in Montenegro-which has some of its settlements built above red bauxite deposits. The radon concentrations were measured in 55 homes in 2002/03, in the summer and winter period, using CR-39 etched track detectors. The average annual radon concentrations were found to be lognormally distributed (geometric mean = 66.2 Bq m(-3), geometric standard deviation = 3.0) within the range from 10 to 966 Bq m(-3), with arithmetic mean of 122.7 Bq m(-3) and median of 61.7 Bq m(-3). Although the annual mean radon concentrations above the action level of 400 Bq m(-3) are found only in four dwellings, the indoor radon levels in the town of Niksic are relatively high when compared with the average in the South European countries, as well as with indoor radon levels in other regions in Montenegro.