Although the press claimed there were dramatic increases in the use of tranquillizers in Northern Ireland after the outbreak of civil unrest in 1969, our data, based on the computerised pricing system for drugs prescribed in the province, showed average annual increases of about 20% from 1966 to 1969, and 10% from 1970 to 1975, thereafter tranquillizer prescribing levels reached a plateau and declined between 1979 and 1980. Total psychotropic drug use also reached a peak in 1975, when about 12.5% of the adult population were estimated to have been receiving such a drug, and declined in the following 5 years. Benzodiazepines accounted for three-quarters of all psychotropic drugs and 98% of tranquillizers prescribed in 1980. Benzodiazepine tranquillizer prescribing has consistently been 20-30% higher than the rest of the United Kingdom, in contrast to hypnotic and antidepressant prescribing which has been consistently lower. The rate of increase in benzodiazepine tranquillizer prescribing over the decade from 1966 was greater than in other European countries, overtaking the level in Norway in 1972 and has since remained third to Iceland and Denmark. Some possible demographic and socioeconomic determinants of these trends are discussed. The prescribing of benzodiazepine hypnotics was almost entirely explained by these variables.