Little attention has been paid to adults pursuing online education at the upper secondary level. The aim of this article is to identify and describe predictors of presence, academic achievement, and satisfaction in online upper secondary education for adults. The study is grounded in the Community of Inquiry (CoI) framework, which is based on three types of presence: teaching presence (TP), social presence (SP), and cognitive presence (CP). A survey was administered to adults who had completed, or were close to completing, an online upper secondary-level course in Sweden, yielding 672 responses. An exploratory factor analysis showed that items from the CP and TP constructs related to peer interaction and teacher guidance loaded onto the SP construct instead. Accordingly, the factors were labeled as individual TP (iTP), extended SP (eSP), and individual CP (iCP) to describe how the CoI framework is manifested in this context, characterized by substantial individual study and varying opportunities for social interaction. Multiple regression models explained a substantial proportion of the variance in iTP (adjusted R2 = .58), eSP (adjusted R2 = .68), and satisfaction (adjusted R2 = .53), a more moderate proportion in iCP (adjusted R2 = .36) and only a small proportion for academic achievement (adjusted R2 = .13). Academic achievement was primarily associated with iCP (β = .38), whereas student satisfaction was primarily associated with iTP (β = .58). Key predictors included course introductions related to studying and technology, tutoring, synchronous online teaching, and collaborative course design.