The aim of this research is to investigate, in a screening population, the relationship between mammographic density and tumour characteristics including size, invasiveness and mammographic features. Mammograms of 105 women with screen detected breast cancer were analysed; 111 lesions were identified. Volumetric density measurements were obtained using Quanta™ and Volpara™. Histological information was extracted from the screening database and radiological features were assessed by two expert breast radiologists. Statistical analysis was performed using Mann-Whitney U test and Spearman’s rank order correlation. The median percentage density by Volpara™ of women with invasive cancers was significantly higher than those with DCIS (6.5 vs 5.0, p =0.046). Similar results were replicated in the Quantra™ measurements, however the results were not statistically significant (17 vs 16, p = 0.19). Further analysis showed a significant positive association between whole tumour size and volumetric density for invasive lesions. Architectural distortion was the only mammographic feature associated with a significant difference in percentage density.