Background Recent research in social epidemiology has established the importance of considering the accumulation of advantage and disadvantage across the life course when examining adult health outcomes. This paper examines (1) accumulation across trichotomous categories of socioeconomic position (SEP), and (2) accumulation in analysis stratified by adult SEP. Methods Data are from the Whitehall II study. Each participant was categorized as having high (0), intermediate (1), or low (2) SEP at three time points in the life course, leading to 27 socioeconomic trajectories. These trajectories were summarized to yield a scale ranging from 0 (high SEP at all three time points) to 6 (low SEP at all three time points). Logistic regression was used to examine odds of incident coronary heart disease (CHD), poor mental and physical functioning, and minor psychiatric disorder. Results There was a graded linear relationship between accumulation of socioeconomic exposure and health. Men with a score of 6 had increased odds of CHD (2.53, 95% CI: 1.3, 5.1), poor physical functioning (2.19, 95% CI: 1.4, 4.1), and poor mental functioning (2.60, 95% CI: 1.4, 4.9) compared with men with a score of 0. In women there was an accumulation effect for CHD and physical functioning. No cumulative effect of SEP on minor psychiatric disorder was observed. The effects of accumulation were weaker in analyses stratified by adult SEP, with early deprivation followed by high adult SEP particularly detrimental for CHD. Conclusions The health effects of socioeconomic disadvantage accumulate over the life course. In addition to accumulation effects, analysis stratified by adult SEP also provided support for the critical period and the pathway model.