We determined the frequencies of null mutations of the FLG gene--2282del4, R501X, R2447X, 3702delG, S3247X, and the 12-repeat allele (rs12730241)--among 460 Caucasians of the city of Novosibirsk, Russia. The frequency was 17.7% for rs12730241, 2.73% for 2282del4, 0.22% for R501X, 0.33% for R2447X, and 0% for 3702delG and S3247X in a western Siberian population. A case-control study showed that the deletion 2282del4 was associated with atopic dermatitis in children (odds ratio 7.01; p<0.001). The other mutations were not.