The rate of contraceptive use in Iran is high, but because abortion is illegal, many unintended pregnancies among married women are likely to be terminated by clandestine and often unsafe procedures, resulting in adverse health outcomes. Drawing upon data from the 2009 Tehran Survey of Fertility, this study estimates the levels and trends of unintended pregnancy and examines determinants of pregnancy intentions for the most recent birth, using multinomial logistic regression analysis. The level of unintended pregnancy decreased from 32 percent in 2000 to 21 percent in 2009, while contraceptive use increased. Unintended pregnancies in the five years preceding the 2009 survey resulted from failures of withdrawal (48 percent) and of modern contraceptive use (20 percent), together with contraceptive discontinuation (26 percent) and nonuse (6 percent). Multivariate findings show that, compared with women experiencing withdrawal failures, the risk of unintended pregnancy was higher among women reporting modern contraceptive failure and lower among those reporting contraceptive discontinuation and nonuse. The high risk of unwanted pregnancy among women experiencing failures in practicing withdrawal or using modern contraceptive methods points to an unmet need for family planning counseling and education rather than to a shortage of contraceptive methods.