Differently from the standard contemporary variety of European Portuguese, in which subject-verb inversion is considered categorical in gerund clauses, in Old Portuguese and Dialectal European Portuguese we can find both subject-verb and verb-subject orders in gerund clauses. These variable word orders challenge classical assumptions that correlate word order in gerund clauses with the null subject parameter. Therefore, other factors have to be taken into account. This work investigates the factors that condition subject-verb word order in gerund clauses of Old Portuguese and Dialectal European Portuguese. Corpus data show us that there is a difference in the frequency of subject-verb inversion in both varieties: verb-subject is the predominant word order in Old Portuguese, while subject-verb is the predominant word order in the dialects, regardless of the presence of inflected gerunds. In what concerns the conditioning factors that may trigger one order or the other, we considered the type of verb, the type of subject, and the presence of a connective. In the dialects, regardless of overt inflection, the most important factor for the post-verbal occurrence of the subject is the type of verb. In contrast, in Old Portuguese subject-verb inversion is the dominant pattern and post-verbal subjects can be found with all verb classes. We hypothesize that differences between the two varieties may correlate with the productivity of gerund clauses introduced by a connective, the specification of the C-domain and information-driven movement.