The objective of this study is to further evaluate the association between asthma and ADHD, addressing issues of familiality in female probands. A case control study of referred ADHD proband girls, controls, and relatives are used. Participants include 140 ADHD proband girls and 122 non-ADHD comparisons, with 417 and 369 first-degree biological relatives, respectively. Relatives are stratified into four groups according to proband ADHD and asthma status. The authors compare rates of asthma and ADHD in relatives. ADHD does not increase the risk for asthma in probands. Patterns of familial aggregation are mostly consistent with independent transmission of ADHD and asthma in families of girl probands. The results extend to female probands' previously reported findings that asthma and ADHD are independently transmitted in families. These findings further support the conclusion that ADHD symptoms should not be dismissed as part of asthma symptomatology or a consequence of its treatment.