Nine hundred three former college freshmen were followed 7 yr after entering college by means of a detailed allergy questionnaire. Original data collected from the students as freshmen, including a history of atopy and allergy skin test results, were evaluated in relation to the frequency of developing new allergies. During the 7-yr follow-up period, new cases of hay fever occurred in 12.6%, nonseasonal allergic rhinitis in 4.8%, and new asthma in 2.5%. The risks of developing asthma and allergic rhinitis are both significantly associated with a prior positive allergy skin test. The risk of developing asthma, not hay fever, is significantly associated with a prior history of atopy. The association of positive allergy skin tests with the development of new cases of allergy remains significant throughout the 7-yr follow-up period. However, individuals who had all negative skin tests developed significantly fewer new cases of clinical allergy during the first 3 yr of follow-up; in the next 4 yr of the 7-yr follow-up, increased numbers of individuals with negative scratch tests developed new cases of allergy. Thus, negative skin tests proved of less prognostic value during the last 4-yr period of this 7-yr study, although significant differences still are apparent between the positive and negative reactor groups.