Predicting adult asthma, using childhood characteristics, is important for advising on prognosis and, potentially, for secondary prevention. A novel use of multivariate likelihood ratios (LRs) to quantify prognosis is described here. Of 718 subjects of a community-based cohort, 575 (80%) members were recruited at age 8-10 yrs and were re-assessed 15-17 yrs later. At baseline, information about symptoms, spirometry, histamine challenge and skin-prick tests were collected. At follow-up "asthma symptoms" were defined as wheeze, sleep disturbance from asthma or inhaled steroid use within the previous year. LRs were calculated for significant predictors of this outcome. Shinkage factors were applied to yield multivariate LRs. Childhood characteristics that independently predicted asthma symptoms in adulthood were obstructive spirometry (adjusted (adj)LR 2.9, 95% confidence interval (CI) 1.3-6.5), airway hyperresponsiveness (adjLR 2.6, 95% CI 1.8-3.7), atopy (adjLR 2.0, 95% CI 1.5-2.7), recent wheeze (adjLR 1.9, 95% CI 1.5-2.5) and being female (adjLR 1.29, 95% CI 0.8-2.1). Children with all five characteristics had a cumulative LR of 36.9 for asthma symptoms in adulthood. Most adults who had asthma symptoms did not have manifestations of asthma as children. However, the presence of obstructive spirometry, airway hyperresponsiveness and atopy in childhood identifies individuals with increased likelihood of having asthma in adulthood. Cumulative likelihood ratios are more valuable than odds ratios for quantifying risk in individuals and for identifying people with most to gain from preventive interventions.