Although patients with semantic deficits can sometimes show good performance on tests of object decision, we present evidence that this pattern applies when nonsense-objects do not respect the regularities of the domain. In a newly designed test of object-decision, 20 patients with semantic dementia viewed line drawings of a real and chimeric animal side-by-side, and were asked to decide which was real. The real animal was either more typical (real > nonreal) or less typical (nonreal > real) than the chimera. Performance was significantly better in the real > nonreal condition, and success in both conditions was modulated by patients' degree of semantic impairment. A similar effect of item typicality was revealed in a subset of items selected from a standard test battery. Object-decision scores were highly correlated with other pictorial and verbal assessments of conceptual knowledge, suggesting that impaired performance on all tasks resulted from the degradation of a unitary underlying system.