This article examines common lexicogrammatical problems found in Cantonese English as a second language (ESL) learners' written English output. A study was conducted with 387 student participants, who were asked to do two untutored and unaided free-writing tasks of about 200-300 words each. A range of lexicogrammatical error types commonly found among Hong Kong Cantonese ESL learners was identified. Errors from the lexical level included vocabulary compensation and inaccurate directionality; errors from the syntactic level included calquing, existential structures, incorrect ordering of adverbials, and independent clauses as subjects; and those from the discourse level included periphrastic-topic constructions. Mother-tongue influence was inevitably an important source of the problems, but inadequate mastery of correct usage of the target language and universal processes were also important factors. The results of the study have potential for enhancing our understanding of the interlanguage grammar of learners and the nature, sources, and prevalence of learner problems. The results also have promising pedagogical implications, as they inform teachers of the levels, nature, sources, prevalence, and gravity of learner errors and equip them with the key ingredients needed for the design of appropriate remedial instructional materials. A discussion of how the taxonomical classification would be useful for language teachers is also given. (Contains 5 footnotes.)