In this talk I will present preliminary results of on-going research on the phonetics and phonology of Shilluk, a Nilotic language spoken in Southern Sudan. While there are a number of studies on the Shilluk sound system (Gilley 1992, 2000; Noske 1995), its rich system of suprasegmental distinctions is not yet well understood. Focusing on the morphology of verbs, I have found evidence for seven distinctive tone patterns (tonemes), and a three-level vowel length distinction (i.e., V vs. VV vs. VVV). This typologically unusual length distinction is also found in closely-related Dinka (Andersen 1987, Remijsen & Gilley 2008). In both languages, we find a lexical distinction between short and long stems, but the two languages differ in the morphological role of the length distinction.