The aim of the study was to assess mortality trends due to road traffic accidents in Poland between 1999 and 2018. The study material was a database including 7,582,319 death certificates of all inhabitants of Poland who died in the analyzed period (104,652 people died of transport accidents). Crude deaths rates (CDR), standardized death rates (SDR) and joinpoint models were used. Annual percentage change (APC) for each segment of broken lines and average annual percentage change (AAPC) for the whole study period were calculated. CDR decreased from 19.7 per 100,000 population in 1999 to 9.6 per 100,000 population in 2018; APC was −4.1% (p < 0.05) while SDR decreased from 20.9 to 10.9 per 100,000; APC was −4.1% (p < 0.05). Large differences in traffic accident-related mortality were observed between men and women. An analysis by gender and age shows that the decline in the number of deaths due to traffic accidents has been slowed down in the oldest age group, 65+, in both males and females. There is a need for in-depth analyses aimed at introducing effective preventive solutions in the field of road traffic safety in Poland. Legal regulations should particularly refer to the most endangered groups of road users.