Objective: The aims of this study were to assess the effects of screening through BreastScreen NSW on the stage of cancer at diagnosis, and differences in cancer stage at diagnosis according to sociodemographic factors. Methods: Using linked BreastScreen NSW screening attendance records and NSW Cancer Registry data, the effects of screening participation and sociodemographic characteristics on stage at diagnosis were investigated using Kruskal-Wallis analysis of variance or the Mann-Whitney U-test for the 2002-13 diagnostic period. Multivariate logistic regression was used to investigate predictors of stage at diagnosis. Results: The association between BreastScreen NSW participation and earlier stage at diagnosis was strongest when the last screening episode occurred within 24 months of the cancer diagnosis, with an odds ratio of localised versus non-localised cancer of 1.61 (95% confidence interval 1.51-1.72). Women aged ���70 years, Aboriginal women, residents of major cities and women living in areas of socioeconomic disadvantage were more likely to have distant than non-distant stage at diagnosis. A trend towards more distant stage in more recent diagnostic years was evident after adjusting for screening participation. Conclusions: The strongest and most consistent predictor of earlier stage at diagnosis was BreastScreen NSW participation. Continued efforts to increase screening participation are important to achieve earlier stage at diagnosis, particularly for sociodemographic groups with more advanced disease. What is known about the topic?: Earlier cancer stage at diagnosis is a prerequisite for mortality reduction from screening. Past research indicated that screening participation in New South Wales (NSW) was strongly associated with early stage at diagnosis and mortality reduction. More contemporary data are needed to monitor screening performance in NSW and assess differences in cancer stage across sociodemographic subgroups. What does this paper add?: Using data linkage, this paper indicates associations between screening, sociodemographic factors and stage at diagnosis for the NSW population in 2002-13. Contrary to expectations, major city residents tended to have a lower proportion of early stage breast cancer at diagnosis, which may be indicative of lower screening coverage and barriers to screening. Compared with past research, similar effects of screening and other sociodemographic factors on the stage of breast cancer at diagnosis were observed. This paper compares screening histories across sociodemographic groups, indicating statistically significant differences. What are the implications for practitioners?: Increasing screening participation is particularly important for sociodemographic groups who are diagnosed at more advanced stages, including women from lower socioeconomic areas, Aboriginal and Torres Strait Islander women and residents of major cities. In particular, the results reinforce the need to further develop targeted strategies to increase screening participation among NSW women from lower socioeconomic areas and Aboriginal and Torres Strait Islander women. Further investigation into screening coverage and barriers to screening for residents in major cities is needed.