Heidi Klum is one of the worlds leading supermodels. She's got quite an entrepreneurial streak as well and is currently hosting a very popular fashion reality TV show; "Germany's Next Top Model". This show has come under attack for promoting extreme thinness in young women. Apparently one of the candidates on the program was told she was too fat even though she only weighed 52 kilograms. But the network running the program believes the criticism is overblown and stated that "Heidi Klum says several times during the show that models must eat sensibly."
So how much does Heidi Klum herself weigh? According to Wikipedia, she weighs 119 pounds (54 kg) and her height is 5 feet and nine and a half inches (177 cm). I think these stats are from her teenage modeling years. I saw another interview dated 1999 where she said she weighed 127 pounds. Who knows what she weighs now in 2006? She still looks super thin, and I would guess she now weighs somewhere in the 130's range.
How much models weigh 'stats' are provided to the modeling agencies by models, and the agencies in turn provide the stats to their clients, but I'm sure models typically advertise themselves as weighing a few pounds less than they actually do. And the modeling agencies wouldn't object to this and aren't about to do public weigh-ins. As long as the models look really great, they don't check to see if they are underestimating their true weight.
Update June 20th 2006: Heidi Klum is pregnant again. US Weekly reports she is expecting her third child. She has a baby boy only 9 months old and a two year-old daughter.