In a randomized double-blind trial 251 adults with sinusitis-like symptoms were given amoxicillin/clavulanate or placebo for 6 days. Seven diagnostic indicators for acute bacterial rhinosinusitis are compared by their accuracy assuming a latent class model and by the treatment effect that they would have had if used to select a subset of patients for antibiotic treatment. Under a latent class model, radiography is a more efficient indicator then C reactive protein (CRP), which is, in turn, more efficient than other clinical signs and symptoms. However, a history of purulent nasal discharge, and signs of pus in the nasal cavity and throat, are better criteria than radiography or CRP for selecting those patients who will benefit from antibiotic treatment. These contradictory results are a salutary reminder that diagnostic indicators need to be evaluated in terms of therapeutic consequences for the patient.