Background: Recent research evidence from the general population has shown that tobacco smoking and raised body mass index (BMI) are associated with worse asthma outcomes. There are indications that asthma morbidity and mortality may be higher among people with intellectual disabilities (ID) than the general population, but the reason for this is not known. This is the first study to investigate the extent of smoking and higher than recommended BMI among adults with ID and a diagnosis of asthma. Method: Health-related data for 1097 adults with ID were collected from 28 primary care practices in Bristol, UK. Results: Prevalence of asthma in this sample of adults with ID was 12% which was much higher than among the general population living in the region. The 132 patients with asthma were found to be nearly twice as likely to be current smokers as patients with ID who did not have asthma (29.5% vs. 15.6%). Smoking rates were higher among men than women with asthma (35.7% vs. 22.6%). Patients diagnosed with asthma were also more likely to be obese (BMI [greater than or equal] 30) than patients with ID but no asthma (42.7% vs. 31.6%). Obesity was particularly a problem among women with asthma as more than half (52.1%) had a BMI [greater than or equal] 30. Conclusions: A very high proportion of patients with ID and asthma were found to be current smokers and/or obese. There is now strong research evidence that both smoking and obesity are implicated in the development of asthma and associated with worse disease outcomes. This study highlights the urgent need for programmes aimed at providing support for people with ID and asthma to stop smoking and to achieve a healthy body weight.