Domestic Psocoptera were sampled in Madrid throughout a complete year (1991-92) by means of sticky traps in bathrooms, kitchens and inside windows. A total of 409 individuals comprising ten species of psocids was caught from 4056 traps inspected fortnightly. The predominant species were Liposcelis decolor, Li. brunnea, Psyllipsocus ramburi, Li. bostrychophila, Li. pearmani, Dorypteryx domestica and Lachesilla pedicularia, in descending order of abundance. Apartments were classified according to eight quantitative variables: age and area of building, level of apartment (i.e. storey), numbers of windows, inhabitants, their pets (birds and mammals), ornamental plants indoors; and two qualitative factors: floor material and presence or absence of trees adjacent to the house. Psocid communities in human habitations were assessed by the island biogeography theory: diversity increased with apartment size and the number of species decreased with building date. Psocid populations were most abundant in bathrooms, which presumably act as sources for dispersal to other parts of the premises. No other significant correlations were found with the other housing factors investigated. Whereas psocids were active indoors during all months of the year, the peak prevalence was in summer, July and August, one or two months ahead of the local seasonal pattern for non-domestic psocids. Although psocids are usually not seriously unhygienic, causing only minor problems of contamination and allergies, this information should help towards their environmental control.