Background Male clients of sex workers are at high-risk of HIV and are a key group in the spread of sexually transmitted infections to the general population. Places undergoing population growth are altering their economic, physical and social environments which may influence the pattern of sexual risk behaviour. However population growth is not uniform within or between U.S. metropolitan areas and there is an interrelated pattern of growth within a metropolitan area. This study examined the association of county population growth that was slower versus similar and faster than its own metropolitan area’s pace of population change with male clients in a sample of men (N = 303) residing in U.S. metropolitan areas embedded in a 1999–2000 national probability telephone survey of STD behavioural measurements.

Methods Population counts for non-institutionalised population at the county level were obtained from the 1990 and 2000 U.S. Census and the total household population in each metropolitan area was calculated by adding the household population of all its component counties. County population change relative to its metropolitan area was quantified using location quotient. Poisson regression was used to obtain prevalence ratio (PR).

Results The prevalence of male clients was 17.5%. In unadjusted analysis, there was no statistically significant relationship between clients and whether the county of residence experienced a rate of growth that was slower versus similar (PR = 1.79, 95% CI 0.9–3.3, P > 0.05) or faster (PR = 1.4, 95% CI 0.7–2.9, P > 0.05) to its overall metropolitan area. After adjusting for county-level demographical differences at the starting period, clients were however more likely to reside in counties that experienced a similar (PR = 2.33, 95% CI 1.1–5.0, P < 0.05) or a faster (PR = 2.5, 95% CI 1.1–5.9, P < 0.05) pace of growth.

Discussion Male clients of sex workers may not be similarly distributed across metropolitan areas and demographic changes may influence patterns of STI risks.