BMI is neglegent to muscle mass.
Muscle weighs more than fat,
there for some one could be 6 foot and 200lbs and that's over weight.
yet it's only with a body fat analysis that you can figure out if they are actually obese (which is a condition of fat not muscle).
for example, most rugby players are categorised overweight or obese by BMI evaluations, even though they are possibly at the peak of ther physical fitness. since the majority of their weight is muscle mass.