Aeroallergen sensitization occurs in most patients with asthma and is noted in a high percentage of patients with mild and moderate asthma. The percentage of those that are atopic with severe asthma appears less, but still approximates the percent seen in patients with mild and moderate asthma. The objective of this study was to review the prevalence of positive skin tests and atopic disease in patients with asthma. A review was performed of the literature with searches to include "skin test and asthma," "allergic asthma," and "allergies and asthma" in both PubMed and Ovid and selected articles that were relative to our objective. Most studies highlight the significances that allergic disease plays in asthma. However, the prevalence of allergic disease in mild to moderate asthma ranges from 50 to 95% and recent data suggest that 95% may be very accurate. In severe asthma the percentage is less, but still recent data suggest it may be as high as 90%. Patients with high IgE, high exhaled nitric oxide (eNO), low provocative concentration of methacholine causing a 20% fall in forced expiratory ventilation in 1 second (PC(20)) and minority ethnicity have a higher number of positive skin tests and presumably are hypersensitive to more aeroallergens. Patients with late-onset asthma are less likely to be allergic; nonetheless, the vast majority even >65 years of age have an allergic component to their disease. Female gender, late-onset asthma, nasal polyps, severe asthma, and, possibly, patients with a reaction to autologous serum injection increases the likelihood that asthma may be nonallergic, as defined by negative skin tests. The vast majority of patients with mild-to-moderate and even severe asthma have an allergic component to their disease. Avoidance, omalizumab, and allergen immunotherapy may be useful in all severities of asthma, even in the elderly, if indicated and not contraindicated. As many as 90-95% of patients with asthma have aeroallergen sensitization and the pattern varies with ethnicity, location of residence, and onset of asthma, but not age. Higher levels of IgE and eNO and lower values of PC(20), are noted in patients with asthma and aeroallergen sensitization.