This paper examines a recurring yet largely unrecognized theme-type in nineteenth-century waltzes, which I term the "waltz period." Building on Caplin's (1998) form-functional theory and taking the theme from Strauss Sr.'s Frohsinns Salven, Op. 163, No. 5 as a point of departure, I show how the waltz period diverges from the typical period in its grouping structure and harmonic progression. Instead of dividing into a basic idea and a contrasting/cadential idea, the antecedent comprises a two-measure basic idea followed by two one-measure fragments through which a cadence emerges. Harmonically, the antecedent phrase frequently employs progressions characteristic of sentence presentations, raising questions about whether a cadence is present at all. Upon restatement of the basic idea in the consequent phrase, however, the V-I progression that closes the antecedent is retrospectively heard as cadential, illustrating Schmalfeldt's notion of formal becoming. Although the consequent phrase in the waltz period frequently repeats the antecedent's exact harmonies and cadence, which is unusual for typical periods, the second cadence is stronger due to the tonic note placement on the downbeat in both the melody and the bass. Far from anomalous, the waltz period appears in Schubert's, Chopin's, and Clara Schumann's waltzes as well. Building on recent extensions of Caplin's form-functional theory, this study broadens the discussion of nineteenth-century phrase structure by examining waltz themes that challenge eighteenth- and nineteenth-century formal paradigms and underlines the waltz's influence on broader compositional practice.