Objective The aim of this multicentre randomised controlled trial was to investigate the contribution of de qi to the immediate analgesic effect of acupuncture in patients with primary dysmenorrhoea and the specific traditional Chinese medicine diagnosis cold and dampness stagnation. Method Eighty-eight patients with primary dysmenorrhoea and cold and dampness stagnation were randomly assigned to de qi (n=43) or no de qi (n=45) groups and underwent 30min of SP6 acupuncture. The de qi group received deep needling at SP6 with manipulation using thick needles; the no de qi group received shallow needling with no manipulation using thin needles. In both groups the pain scores and actual de qi sensation were evaluated using a visual analogue scale for pain (VAS-P) and the acupuncture de qi clinical assessment scale (ADCAS), respectively. Results Both groups showed reductions in VAS-P, with no signficant differences between groups. ADCAS scores showed 43/43 and 25/45 patients in de qi and no de qi groups, respectively, actually experienced de qi sensation. Independent of original group allocation, VAS-P reductions associated with actual de qi (n=68) were greater than those without (28.418.19mm vs 14.612.28mm, p=0.008). Conclusions This study showed no significant difference in VAS-P scores in patients with primary dysmenorrhoea and cold and dampness stagnation immediately after SP6 acupuncture designed to induce or avoid de qi sensation. Both treatments significantly reduced VAS-P relative to baseline. Irrespective of group allocation, patients experiencing actual de qi sensation demonstrated larger reductions in pain score relative to those without, suggesting greater analgesic effects.