Introduction: Radiography of lumbar spine is classified as a relatively high dose examination in classical radiography. There is a simple but effective way to reduce the radiation dose, namely the replacement of the anteroposterior (AP) imaging projection into the posteroanterior (PA) projection. Purpose: The purpose is to determine how dose of radiation in X-ray examination of lumbar spine is changed when using the PA projection and does the PA projection have influence and change the image quality compared to the AP projection. Methods: The research was carried out in two parts. In the first part of the study we measured the dose (DAP) on the phantom, where we made 5 images in the AP and 5 images in the PA projection. The second part of the study was carried out on the 100 patients, randomly divided into two groups of 50. We took images of one group in the AP and the other in the PA projection. For all patients, we recorded the mass and height for the body mass index (BMI), and at the same time we compared the size of the field, the thickness of the abdomen, DAP and the effective dose. On the end, all radiographs were evaluated independently by three radiologists. Results and discussion: A study on the phantom showed that the field at the PA projection was 62,6 cm2 larger compared to average values of the AP projection (p = 0,310). The AP projection was even better with DAP by 1,9 μGy m2 (p = 0,310) and at the evaluation of radiographs by 0,2 (p = 0,690). The measurement of the effective dose was lower by 0,033 mSv for PA projection, where statistically significant differences were found (p = 0,008). Measurements on the patients showed that the field was larger with a PA projection by 8 cm2 (p = 0,391). The thickness of abdomen was reduced by 2,4 cm (p <10-3) in the PA projection, as did DAP by 16,3 μGy m2 (p = 0,009) and the effective dose by 0,09 mSv (p <10-3), which means that the differences were statistically significant. The estimation of radiographers was 0,1 higher for PA projection, but there were no statistically significant differences between the estimates (p = 0,690). Conclusion: The results showed that the use of PA projection of lumbar spine reduces DAP (26,7 %) and effective dose (53,3 %) while preserving the image quality, so we can conclude that the imaging of lumbar spine in PA projection is recommended method of selection.