BMI and body fat percentage are not the same thing. BMI, or Body Mass Index, is simply a rewarmed version of the standard height weight tables, in which you do some sort of calculation of height and weight to develope an index over and under which you should not go to be healthy. It does NOT factor in the composition of whatever comprises your "weight" (i.e. body fat, lean muscle mass, skeletal mass, vital organs, water, etc.) nor does it factor in body type and thus, IMHO, is precisely useless as a piece of information.
Body fat percentage is a calculation of how much body fat (storage fat and essential fat) a person has in relation to her total body weight. It is, perhaps, a more important measurement of one's overall healthy body composition, because excess storage fat (in CLINICAL terms, not Shape Magazine terms) is a proven health risk. It's far more complicated to measure body fat percentage, but it's a bit more useful.
A-Jock