The primary sign of menstruation is the appearance of a bloody discharge from the vagina. Menstrual blood may be bright red, light red, or a much darker brown or black-appearing. The color depends on the rate at which the bleeding occurs. Slower bleeding tends to causes the color to become darker. Normal menstrual blood may be thin and watery, or thick and stringy and may even contain clumps or clots of blood.

Another common symptom of menstruation is menstrual cramps. When the uterus contracts to help shed the uterine lining, these contractions can cause painful abdominal cramping. These cramps can range from a dull ache to sharp, stabbing pains in the abdomen or back. Menstrual cramps often decrease in severity with age and may disappear completely.  

Other symptoms that can occur during menstruation include abdominal bloating (an uncomfortable feeling of fullness and distension in the abdomen), headache, and breast tenderness.