BACKGROUND: Arterial hyperflow to haemorrhoids has been implicated as a possible pathophysiological co-factor in haemorrhoidal disease. The purpose of this study was to investigate how transanal haemorrhoidal dearterialization (THD) can influence haemodynamic parameters at the level of the haemorrhoidal piles. METHODS: Patients with grade III haemorrhoids selected for THD between July and December 2018 were evaluated using endoanal ultrasonography and colour Doppler imaging at the level of internal haemorrhoids before and 1 year after the surgical procedure. Peak systolic velocity, pulsatility index, resistivity index, acceleration time, and end-diastolic velocity were measured, and preoperative and postoperative values compared. Symptom severity was measured using a symptom-based questionnaire (score range 0-20). RESULTS: Of 21 patients treated, 17 completed the study. Compared with preoperative values, postoperative peak systolic velocity (mean(s.d.) 18.7(1.1) versus 10.3(0.4) cm/s; P < 0.05), pulsatility index (5.5(0.3) versus 2.8(0.4); P < 0.050), and resistivity index (1.0(0.2) versus 0.8(0.5); P < 0.050) decreased significantly, whereas acceleration time increased significantly (65.6(3.6) versus 83.3(4.7) cm/s2; P < 0.050); end-diastolic velocity did not change (1.9(0.2) versus 2.0(0.4); P = 0.753). Symptoms disappeared or had improved significantly in all patients by 1 year after surgery. The mean(s.d.) total symptom severity score decreased from 15.8(1.1) to 1.2(1.6) (P < 0.001). CONCLUSION: THD affects the main haemodynamic parameters at the level of internal haemorrhoids and is associated with a decrease in arterial hyperflow.