The paper reports on the results of a pilot study that investigates spelling proficiency in heritage language writers of Russian (with American English as the dominant language). Until recently, spelling was viewed as a trivial aspect of literacy development in heritage learner language research (Llombart-Huesca, 2017). However, the wealth of research on the acquisition of orthography from the field of child language development (both mono- and bilingual) has highlighted orthography as a fundamental aspect of literacy development that connected to such important linguistic skills as phonological knowledge and awareness, and understanding of morphological structures. Spelling skills also depend on the knowledge of spelling conventions of a specific language, which require extensive practice with reading/writing in the language. The goal of the paper is to provide an initial qualitative analysis of misspellings in Russian heritage data with an aim to begin addressing the gap in the research literature and to hypothesize on the role of the underlying linguistic knowledge that result in spelling idiosyncrasies in heritage data. The data for the study are drawn from the heritage sub-corpus of the ACTR Essay corpus (Kisselev, 2019) which contains essays collected from Russian learners at different proficiency levels from across the U.S. 120 heritage learner essays were subjected to the Writing Proficiency Test to obtain independent proficiency ratings. All words spelled in a non-standard way were tagged and extracted for analysis. Orthographic errors were then categorized based on the probable cause of deviation, i.e., phonological, morphological, and convention-based. The types of errors were then correlated with proficiency levels. The patterns observed in the distribution of types of spelling errors will be discussed in light of the nature of heritage language. The paper will also discuss how this research may inform heritage language teaching and learning.