If you're not pregnant, your ovaries are probably failing to release an egg (anovulation), which means your body won't produce the hormones that guide menstruation. Stress can trigger anovulation, and doctors don't typically worry if it happens just once or twice a year. In older women, a "missed" period may also simply be a very long cycle. Experts say that when you see a 60-day cycle, that's a good indication you're approaching menopause.
Talk to your doctor if you miss more than two periods (and you're not perimenopausal) or have other symptoms such as irregular bleeding. Polycystic ovary syndrome (PCOS) occurs in about 10 percent of women of childbearing age (women who are obese or have insulin resistance seem to be at higher risk). This condition can cause extreme hormonal swings, missed periods, infertility, thinning hair, and other health concerns.