Undergraduates participated in 3 speeded naming experiments investigating the effect of onset cluster complexity on response latency. Words with complex onsets (e.g., spin) had shorter response latencies than words with simple onsets (e.g., sin), despite the fact that words with complex onsets had more letters and phonemes but fewer neighbors, properties previously found to increase naming latency. Moreover, the magnitude of the effect depended on the particular complex onset. These onset complexity effects can be explained by the constraint imposed by the 2nd letter on the 1st letter and 1st phoneme for words with an onset. This constraint ultimately arises because phonemes increase in sonority from the beginning of the syllable to the nucleus. Dual-route models cannot account for these results, but analogy and parallel distributed models can, if the criterion to initiate articulation is based on the initial phoneme.