It has been suggested that manual sign systems designed to represent English are unlearnable because they are not natural languages. In order to examine this premise, the present study examines reading achievement and expressive English skills of 13 profoundly deaf students, aged 7;1 to 14;8, who were educated using only a manually coded English (MCE) sign system. Linguistic structures selected for analysis were designed to reflect unique characteristics of English, as well as those common to English and American Sign Language, and to obtain a broad picture of English skills. Results showed that the deaf students had expressive English skills comparable to a hearing control group for some features of English that reflected syntactic and lexical skills. They showed substantial deficits in inflectional morphological skills that were not predictive of the complexity of their language. The results reveal which aspects of MCE appear to be learnable and which appear problematic for deaf students.