Writing performance is greatly affected by task-related elements such as topic familiarity, difficulty, task-type, and subject matter of the prompt, which are perceived differently by each individual writer. Yet, little has been reported on the direct relationship between writers' perceptions of a prompt and their actual performance on the prompt. The present study explored possible associations between students' perceptions of a writing prompt and their actual writing performance on a field-specific (FS) English for academic purposes (EAP) writing test, compared to those on a general-topic test. Each of the 124 students produced two writing samples, one on an assigned regular topic and the other on one chosen from the four FS prompts. The writers also responded to a survey of their perceptions of the FS prompts and the FS test in general. The subjects' performances on the two tests were compared across the four prompt subgroups, and analyzed against their survey responses. It was found that students' performances were not statistically different on the two different tests or across the prompts chosen on the FS EAP writing test. Further analysis revealed that student subgroups varied in their perceptions of the degree of prompt familiarity. Based on the results, future research implications are proposed for EAP testing and L2 writing research. (Contains 10 tables.)