In this paper, authors estimate long-term distributions of wave induced bending deflections of three ships including a dry cargo ship, a bulk-carrier and a destroyer. The extreme values in the long-term distributions of midship deflections, the probability of exceeding the value is equal to 10^-8, range from L /1000 to L /500. The values are larger than those in still water which are expected to be smaller than L /1000 in usual case from a result of measurment on 28 ships, which have length from 120 m to 160 m and belong to the same group as the above three vessels in their size. It is also remarkable that the values scatter widely. Authors study on the character of the extreme and clarify that design wave bending stress, ship length, ratio of ship length to depth, fineness of hull form, and structure type have effects on the deflection. So it is impossible to keep the deflection in a range by keeping only design stress in a given value. From the study authors develope a method of estimating the extreme midship deflection with very small erorr provided the extreme value of wave induced bending moments is known. And in appendix authors show an improved method of calculating bending deflection at midship from values of bending moment at three positions which divide ship length into four equal parts.