Aim. In the present study, we aimed to examine the effect of the length of the introducer during transradial therapeutic and diagnostic endovascular interventions on the incidence of the radial artery occlusion (RAO).Methods. Patients (n = 100) who underwent coronary angiography and/or percutaneous coronary intervention with a transradial approach were enrolled in the study. The patients were randomised into two groups. The first group comprised 50 patients who underwent transradial coronary angiography and/or percutaneous coronary intervention using a long introducer (6Fr, 25 cm; Radifocus Introducer II, Terumo, Japan). However, one patient was excluded from the analysis due to an emergency transfer to another hospital and was not considered in the comparison of outcomes (n = 49). The second group comprised patients who underwent transradial endovascular procedures using a short introducer (6Fr, 10 cm; Radifocus Introducer II, Terumo, Japan) (n = 50). The primary endpoint of the study was the rate of the RAO according to the Doppler ultrasound findings. The secondary endpoints included post-puncture haematomas, radial artery perforation/dissection, neuritis of the median nerve, puncture site bleeding, the rate of needle-type conversion, puncture time, procedure from the introduction of the introducer to its extraction, time of fluoroscopy and total air kerma rate. A comparative analysis of the patency of the radial artery during the hospital stay was performed according to the Doppler ultrasound findings.Results. The average age of the patients was 60.7 ± 10.6 years. An analysis of the primary endpoint of the study showed no statistically significant differences in the incidence of the RAO in both observation groups (8.2% vs. 4.0%; p = 0.436). An analysis of the secondary endpoints showed no difference in the rate of post-puncture haematomas (16.3% vs. 16.0%; p = 0.965) or local bleeding (2.0% vs. 0.0%; p = 0.310). In addition, no complications such as perforation/dissection of the radial artery or neuritis of the median nerve were noted. However, an increase in the needle-type conversion rate was noted for patients in the long introducer group (10.2% vs. 0.0%; p = 0.027). An increase in the duration of puncture was demonstrated (94 [67.5; 162.5] s vs. 42.5 [33.0; 65.3] s; p < 0.001) and the procedure itself when using a long introducer (448.0 [337.5; 633.0] s vs. 350.5 [307.0; 506.8] s; p = 0.04). At the same time, the duration of fluoroscopy (82.0 [48.5; 133.0] s vs. 69.5 [48.0; 118.3] s; p = 0.672) and the total air kerma rate did not statistically differ (140.8 ± 97.7 mGy vs. 128.2 ± 71.3 mGy; p = 0.721).Conclusion. The use of long introducers did not demonstrate advantages in the incidence of RAO development compared with the use of short introducers. However, the puncture time and duration of endovascular coronary procedures with the use of long introducers were longer than in the group where the short introducers were used. Furthermore, the time of fluoroscopy and total air kerma rate did not statistically differ.linicalTrials.gov Identifier: NCT03854253Received 29 May 2019. Revised 12 August 2019. Accepted 29 August 2019.Funding: The study did not have sponsorship.Conflict of interest: Authors declare no conflict of interest.Author contributionsConception and study design S.S. Sapozhnikov, I.S. BessonovData collection and analysis: S.S. Sapozhnikov, I.S. Bessonov, I.P. Zyrianov, D.V. Krinochkin, T.N. Baskakova Drafting the article: S.S. SapozhnikovCritical revision of the article: I.S. BessonovFinal approval of the version to be published: all authors