Irregularity in vaginal bleeding patterns is the most common clinical side effect causing discontinuation of the method reported by the-users of the newer contraceptive methods, especially hormonal ones. An objective assessment of vaginal bleeding pattern is, therefore, critical in evaluation of a new contraceptive method for its acceptance and continued use. The menstrual diary records of women participating in clinical trials of several contraceptive methods undertaken by the Indian Council of Medical Research were analysed. It was observed that the long-acting progestogen-only hormonal contraceptives like levonorgestrel (LNG)-releasing subdermal implants Norplant or intrauterine devices (LNG-IUD) as well as injectable contraceptive NET-EN 200mg given 2 or 3 monthly produced disturbances in bleeding pattern in the majority of their users. Very heavy or prolonged bleeding, a potential health hazard was uncommon and a shift more towards infrequent bleeding was observed. In Norplant-II implants users, 75 to 80% of women had irregularities in bleeding pattern during the first year of use which improved with prolonged use. However, even at 4 years of use, about half of the users of Norplant-II implants continued to have irregular bleeding patterns. The bleeding disturbances occurred in 80% users of 200mg NET-EN injectable contraceptives also during first year of use, however unlike Norplant-II implants users, there was no improvement with prolonged use. Combined monthly injectable contraceptives containing 50mg NET-EN and 5mg estradiol valerate caused less bleeding problems with half of the users experiencing normal pattern during one year of its use. Combined low-dose oral pills, both triphasic and monophasic, produced much better cycle control as compared to any of the other hormonal contraceptive-treated groups; about 90% of combined oral pill users had normal bleeding patterns during one year of method use. The use of copper IUDs was associated with increased bleeding in 18 to 20% of women during the initial period of three months which improved with prolonged use. It was observed that the women having frequent or prolonged bleeding had discontinued the contraceptive method more often as compared to those having delayed bleeding episodes or oligomenorrhoea. However, discontinuation rates due to bleeding irregularities at one year were lower in Norplant-II implants users as compared to other long acting hormonal contraceptive methods such as injectables or IUDs in spite of similar or better bleeding patterns in women using these methods.(ABSTRACT TRUNCATED AT 400 WORDS)