What can cause delayed menstrual period?

The list is long: Always check for pregnancy. Other causes: chronic illness, acute weight changes, endocrine disorders, stress - just to name a few.

Delayed period: Reasons for missed/late periods: low body weight, obesity, marked weight ^ or v, over-exercise, endurance athletics, breast-feeding, ^ stress, illness, eating disorders (bulimia or anorexia), anovulatory cycle (no egg released), travel, hormone irregularities, drug use, meds (i.e., birth control) or medical problems. #1 reason is pregnancy.