The florid positive symptoms of schizophrenia (hallucinations, delusions, grossly disordered thinking) are often obvious. By comparison, negative symptoms (flattened affect, impoverished speech, apathy, avolition, anhedonia) are subtler and more difficult to recognize and diagnose. However, there is increasing recognition of the importance of negative symptoms in patients with schizophrenia. Secondary negative symptoms attributable to such factors as unrelieved positive symptoms, the adverse effects of antipsychotic pharmacotherapy, or social isolation may subside with resolution of such factors. In contrast, primary negative symptoms are an intrinsic aspect of schizophrenia; they are persistent and have been associated with poorer clinical outcomes. Although the lack of a reliably effective treatment for negative symptoms is a serious unmet need in this patient population, accurate diagnosis is still important. Assessment of suspected negative symptoms, using validated rating scales, can help to rule out comorbid affective or cognitive disorders that may mimic negative symptoms and to distinguish primary negative symptoms from potentially reversible secondary negative symptoms. This article reviews the definitions and classification of negative symptoms, compares the tools available for their assessment, and offers practical clinical algorithms for sorting through the differential diagnosis.