The aim of the present study was to determine the efficacy of vaginal progesterone in asymptomatic women with a sonographic short cervix (B25 mm) at 18-24 weeks of gestation in reducing the risk of preterm birth. It was a prospective observational study carried out on 60 pregnant women attending the antenatal clinic in tertiary health institute between 18 and 24 weeks of gestation with ultrasonographically-measured short cervix. The women with cervical length B25 mm were alternately divided into two groups of 30 each. Group I was given 200 mg vaginal micronized progesterone capsules and Group II was managed expectantly. Primary outcome was measured as spontaneous birth before 34 weeks of gestation. Secondary outcome was birth at \32 weeks, \37 weeks and the neonatal outcome. The demographic profile of women in both the groups was similar. The rate of spontaneous delivery before 34 and 37 weeks of gestation was significantly less in the progesterone group (3 vs 20 %; p = 0.044, 6.6 vs 26.7 %; p = 0.038). There was no difference in birth weight \2500 g and Apgar score \7 at 5 min in neonates of both the groups. Progesterone was associated with a significant reduction in composite neonatal morbidity (6.7 vs 33.3 %; p = 0.020). There were no serious adverse events associated with the use of progesterone. Thus, in a woman with short cervical length, vaginal progesterone significantly lowers the preterm birth rate and composite neonatal morbidity.