During the recent years there is a rise in prevalence of asthma and other allergic diseases. Simultaneously the number of overweight patients with increased value of body mass index (BMI) rises. It seems that although pathomechanisms of asthma and obesity are different, there is a common pathogenic link in development of these diseases. The influences of environmental, dietary, genetic and infectious factors are taken under consideration. Most epidemiological surveys confirm connection between overweight, obesity and risk of asthma at children and adults. The influence of high birth weight and higher gains of body mass during the first year of life is frequently highlighted. In contrast the risk of allergic rhinitis and allergic conjunctivitis is in negative correlation with body mass. No relation is observed between obesity and allergic dermatitis prevalence. Adipose tissue as an endocrinous organ produces number of cytokines, hormones, and growth factors. It is a source of proinflammatory factors such as: IL-6, TNF-a, TGF-b, leptin, resistin. Adipocytes produce leptin which level stays in positive correlation with adipose tissue mass. Leptin can exacerbate inflammatory process and probably plays an important role in development of lungs. Higher serum level of leptin is considered as a prognostic factor of asthma evolution. Adiponectin has anti-inflammatory abilities and its level is decreased in obesity. There is a negative correlation between concentration of adiponectin and BMI. Also resistin, aP2 protein, and Chilfemale sex hormones take part in development of asthma in obese patients. Influence of genetic factors is still not well known. Since now there were isolated four chromosomic regions, which had connection with higher susceptibility for both: obesity and asthma. Protective effects have dietary factors such as antioxidants and microelements. Obesity deteriorates course of the asthma, exacerbates its symptoms and coexists with other diseases such as obturative sleep apnoea or oesophageal reflux. In coexistence of obesity and asthma, apart from pharmacological treatment of patients, reduction of body mass should be strongly recommended.