Selective mutism (SM) occurs when a child persistently lacks speech in some social situations but not in others, despite the ability to use and comprehend language. While considered to be related to anxiety, SM is poorly understood and studies of SM children are often based on parent reports. This study developed a unique, non-verbally based assessment protocol for SM children in order to better characterize their clinical profile, language abilities, and learning abilities. A comparison was done with a group of children of similar age, with social phobia (SP) but no SM, to search for characteristics that might distinguish SM from other anxiety disorders. Twenty-three children participated in the study (14 SM and 9 SP). The assessment protocol included standardized anxiety rating scales, cognitive and academic tests, and a speech and language assessment. SM and SP groups showed similar levels of anxiety and academic ability, but the SM group showed some language impairments relative to the SP group. Though requiring replication with a larger sample and nonclinical comparison group, the results suggest that SM children can be assessed by non-verbal means and that their disorder is characterized by anxiety and subtle language impairments. Depression and Anxiety 18:153–161, 2003. © 2003 Wiley-Liss, Inc.