This study sought to better understand the prevalence of concurrent and specific difficulties in reading fluency and vocabulary among adolescents with low reading comprehension. Latent class analysis (LCA) was used to identify a sample of 180 students in sixth through eighth grades with reading comprehension difficulties. A subsequent LCA identified subgroups of students with common patterns of strengths and weaknesses in reading fluency and vocabulary. Results indicated that more than 96% of the students demonstrated deficits in at least one area, with the largest subgroup exhibiting co-occurring difficulties in fluency and vocabulary. Difficulties in fluency were more common than difficulties in vocabulary. Students with low reading comprehension but adequate scores in reading fluency or vocabulary represented only a very small portion of the sample. Coupled with findings from prior studies, results indicate that large numbers of adolescents with reading comprehension difficulties are likely in need of intervention in foundational skill and knowledge areas, which may not be viewed as instructional priorities among secondary educators.