The current paper presents information from a survey of the practices associated with the control of ectoparasites on sheep in Northern Ireland in 2005, including the estimated total quantities of pesticide active ingredients used. It also provides comparative data to that obtained from previous surveys in 1981 (Jess & Marks 1986), 1988 (Foy et al.1995) and 1997 (Jess et al.2000). The total number of sheep farms in Northern Ireland decreased by 25% to 8822 farms with a consequent 26% reduction in total sheep population to 2·1 million sheep compared with the previous survey in 1997. During this period, the number of sheep treated for ectoparasites decreased by 40%. The total quantity of organophosphorus (OP) compounds used for ectoparasite control decreased by approximately 67%, from 7·8 tonnes in 1997 to 2·6 tonnes in 2005, during which an estimated 0·38 of all sheep treated for ectoparasites received the OP active ingredient diazinon. The survey results indicate a decline in the practice of plunge-dipping sheep for ectoparasite control with the proportion of farms using this treatment method decreasing from 0·58 to 0·16 between 1997 and 2005. In 1997, an estimated 0·8 of all sheep treated for ectoparasites in Northern Ireland were plunge-dipped, which reduced significantly to 0·28 during 2005. Conversely, the use of alternative methods has increased with pour-on formulations of insecticides, macrocyclic lactones and growth regulators being applied to 0·33 of all sheep treated in 2005 compared with 0·09 in 1997. Use of intramuscular or subcutaneous injections of macrocyclic lactones for ectoparasite control has also increased to 0·24 of all sheep treated in 2005 compared with 0·1 in 1997. The proportion of sheep treated in communal spray showers also increased from 0·01 in 1997 to 0·14 in 2005. Control of blowfly maggots (Lucilia spp.) and prevention of sheep scab (Psoroptes ovis) were the main reasons given by farmers for sheep treatments. On the farms that plunge-dipped, an estimated 0·68 of surplus dip wash was disposed of immediately after dipping took place, with 0·8 of farms emptying the dipping tanks using a vacuum tanker and 0·54 spreading the surplus dip wash directly onto land. An estimated 0·35 of these farmers mixed the dip wash with slurry pre-disposal. The survey suggests that the products used for spray showers are those recommended for plunge-dipping as there are no contemporary products recommended for use in spray showers. Macrocyclic lactone injections recorded in the survey had the dual function of controlling both endo- and ectoparasites.