Respondent incentives are increasingly used as a measure of combating falling response rates and resulting risks of nonresponse bias. Nonresponse in panel surveys is particularly problematic, since even low wave-on-wave nonresponse rates can lead to substantial cumulative losses, and if nonresponse is differential, may lead to increasing bias across waves. Although the effects of incentives have been studied extensively in cross-sectional contexts, little is known about cumulative effects across waves of a panel. We provide new evidence about the effects of continued incentive payments on attrition, bias and item nonresponse, using data from a large scale, multi wave, mixed mode incentive experiment on a UK government panel survey of young people. In this study, incentives significantly reduced attrition, far outweighing negative effects on item nonresponse in terms of the amount of information collected by the survey per issued case. Incentives had proportionate effects across a range of respondent characteristics and as a result did not reduce attrition bias. The effects of incentives were larger for unconditional than conditional incentives and larger in postal than telephone mode. Across waves, the effects on attrition decreased somewhat, although the effects on item nonresponse and the lack of effect on bias remained constant. The effects of incentives at later waves appeared to be independent of incentive treatments and mode of data collection at earlier waves.