Background: The infection frequency among donors found eligible for donation (based on donor questionnaire and physical examination) and therefore the risk of post-transfusion adverse reactions has been demonstrated to be closely related to donor demographics. The aim of the study was to determine the demographic changes among Polish blood donors found eligible for donation and subjected to screening for infectious markers in the years 2005–2018. The results were referred to transfusion safety, and particularly to the risk of transfusion-transmitted infectious agents. Material and methods: Subjected to analysis were data collected i.a. to assess the epidemiology of blood-borne infectious agents: the number of screened donors found eligible for donation divided into categories by sex, first and repeat donation as well as age groups (≤ 20, 21–30, 31–40, 41–50, 51–60 and > 60 years). Frequencies (fraction) were expressed as percentage with a 95% confidence interval [95%CI] and the differences — as percentage point (p.p.). The significance of difference (p < 0.05) was verified by the Chi-squared test, and the Spearman correlation coefficient (R) was used to assess the trend. Results: Most donors were men (74.07% on average) but in the years 2005–2012 the number of women increased by 7 p.p. up to 27.42% [27.30–27.53%] (p < 0.05); by 10.58 p.p among first-time donors and by 7.19 p.p. among repeat donors. The highest frequency of women was observed in the population of the youngest age group (36.02% [35.95–36.09%]) and the lowest among the oldest age group of donors (14.14% [13.80–14.48%]) (difference 21.88 p.p.; p < 0.05). The majority were repeat donors (66.78% on average). The frequency of repeat donors increased by a total of 19.83 p.p. (p < 0.05): by 20.6 p.p. for men and by 21.15 p.p. for women (p < 0.05 for both groups). In all age groups, except the youngest, the majority (p < 0.05) were repeat donors. The frequency of repeat donors increased in subsequent age groups — from 36% in the youngest (≤ 20 years) to 87% in the oldest donors (> 60 years). The frequencyof donors > 40 increased by 11.58 p.p. from 37.38% to 48.96%. Conclusions: In the years 2005–2018, significant demographic changes were observed in the population of Polish donors; the frequency of women donors and repeat donors increased, with benefit for transfusion safety.