Multiple sexual partnerships are a driver of the HIV epidemic in southern Africa. Five linked cluster surveys in 2002, 2005, 2006, 2007 and 2008 allowed us to measure changes in rates of multiple partnerships in these clusters in Swaziland. We selected a stratified random sample of census enumeration areas in 2002 and survey teams subsequently revisited this same sample (a random sub-sample in 2005 and 2006). For this study, analysis includes only people aged 18-29 years interviewed in communities included in all five surveys (1862 men and 2701 women). Among men, there was a significant fall in the proportion having multiple partners in the last 12 months (MP12), among those that had any, between 2002 (61%) and 2007 (46%), followed by a slight rise in 2008 (49%). For multiple partnerships in the last six months (MP6 - measured in 2005 and 2006), there was a decrease between 2005 (43%) and 2006 (25%). There was a significant decrease in multiple partnerships in the last month (MP1) between 2005 (35%) and 2006 (16%), followed by an increase in 2007 (24%) and 2008 (25%). Among women, there was a significant decrease in MP12 between 2002 (22%) and 2007 (9%), then a significant increase in 2008 (15%). There was little difference in women's MP6 between 2005 (7%) and 2006 (6%). There was also little change in women's MP1 between 2005 (5%) and 2006 (3%), with an increase from 2007 (3%) to 2008 (6%); the 2006-2008 difference was significant. A 2006 campaign to reduce multiple partnerships may have changed behaviour among men or it may have made them less likely to admit to multiple partners. The recent increase in MP12 and MP1, especially among women, may reflect behaviour or it could reflect increased willingness to report.