Purpose: Sunitinib in combination with docetaxel enhances antitumor activity in xenograft models of human breast and non-small cell lung cancer. We assessed the maximum tolerated doses (MTDs), safety, pharmacokinetic profiles, and preliminary efficacy of sunitinib plus docetaxel in patients with advanced solid tumors. Methods: In this phase I study, successive patient cohorts received sunitinib 25, 37.5, or 50 mg/day for 4 weeks of a 6-week cycle (Schedule 4/2, 4 weeks on, 2 weeks off) or for 2 weeks of a 3-week cycle (Schedule 2/1, 2 weeks on, 1 week off) with docetaxel 60 or 75 mg/m2 IV q21d to determine the MTDs of this treatment combination. Results: Fifty patients enrolled: 10 on Schedule 4/2 and 40 on Schedule 2/1. MTDs were established as sunitinib 25 mg on Schedule 4/2 with docetaxel 60 mg/m 2 q21d, and as sunitinib 37.5 mg on Schedule 2/1 with docetaxel 75 mg/m2 q21d. On Schedule 2/1, the most frequent doselimiting toxicity was neutropenia (±fever; grade [G]3/4, n = 5) and the most common G3/4 non-hematologic adverse event (AE) was fatigue (G3, n = 8). Hematologic AEs were managed with growth factor support in 11 of 23 (48%) patients treated at Schedule 2/1 MTD. Three patients achieved a partial response at the Schedule 2/1 MTD. There were no pharmacokinetic drug-drug interactions with either schedule. Conclusions: Oral sunitinib 37.5 mg/day on Schedule 2/1 with docetaxel 75 mg/m2 IV q21d is a clinically feasible regimen with a manageable safety profile, no pharmacokinetic drug-drug interactions, and shows antitumor activity in patients with advanced solid tumors. © The Author(s) 2009.