Dysmenorrhoea is painful menstruation that occurs in 45-72% of all women. This was a prospective randomised study of the efficacy of etoricoxib (Arcoxia) compared with mefenamic acid (Ponstan) in treating primary dysmenorrhoea. All single, sexually inactive women with primary dysmenorrhoea were randomised into two groups (mefenamic acid and etoricoxib) of pain relief and underwent a cross-over study. The success of treatment as evidenced by pain relief, the side-effects and complications were observed and analysed. Some 80% (20 women) had significantly better pain relief with etoricoxib, compared with only 20 per cent in the mefenamic acid group (p = 0.007). Etoricoxib has significantly fewer side-effects compared with mefenamic acid (p = 0.005) with significantly reduced menstrual blood loss (p = 0.025). In conclusion, etoricoxib is a better treatment for primary dysmenorrhoea with better pain relief, less menstrual blood loss and fewer side-effects compared with mefenamic acid.