The interplay between self-regulation related skills and language is well recognized in dynamic theories, but few empirical studies have tested it, especially in toddlers. The current study examines the bidirectional links between self-regulation related skills and expressive vocabulary in a longitudinal study during toddlerhood. Participants were 268 toddlers (M[subscript age] = 29.6 months, SD = 4.2; 52% boys), mostly of Portuguese nationality, with medium to high sociocultural and economic status, attending private for-profit and nonprofit facilities in Portugal. Self-regulation (executive function and effortful control) and expressive vocabulary were assessed across three assessment waves. Results from cross-lagged panel models suggested bidirectional links between self-regulation and expressive vocabulary across the three assessment waves. These findings add to previous research by taking a first step into establishing the early onset of the intertwined development of these two foundational skills.