Getting the mebendazole dose right depends entirely on which worm you are treating. Pinworm needs a single 100mg dose repeated at 2 weeks — not a 3-day course. Roundworm and hookworm need twice-daily 100mg for 3 days or a single 500mg dose. This guide covers every dose, children's dosing, 100mg vs 500mg comparison, and the most common dosing mistakes.