Objectives The aim of this study was to quantify the radiation dose reduction during coronary angiography and percutaneous coronary intervention (PCI) through removal of the anti-scatter grid (ASG), and to assess its impact on image quality in adult patients with a low body mass index (BMI). Methods A phantom with different thicknesses of acrylic was used with a Westmead Test Object to simulate patient sizes and assess image quality. 129 low BMI patients underwent coronary angiography or PCI with or without the ASG in situ. Radiation dose was compared between both patient groups. Results With the same imaging system and a comparable patient population, ASG removal was associated with a 47% reduction in total dose-area product (DAP) (p < 0.001). Peak skin dose was reduced by 54% (p < 0.001). Operator scatter was reduced to a similar degree and was significantly reduced through removal of the ASG. Using an image quality phantom it was demonstrated that image quality remained satisfactory. Conclusions Removal of the ASG is a simple and effective method to significantly reduce radiation dose in coronary angiography and PCI. This was achieved while maintaining adequate diagnostic image quality. Selective removal of the ASG is likely to improve the radiation safety of cardiac angiography and interventions.