The aryl hydrocarbon receptor (AhR) is a ligand-activated transcription factor responsive to both natural and man-made environmental compounds. AhR-mediated changes in gene expression frequently affect cell growth, and recent evidence reveals a direct role for the AhR in cell cycle control. This review examines the functional interaction between the AhR and the retinoblastoma tumor suppressor protein (pRb), and its impact on the G1 phase of the cell cycle. The discussion emphasizes gaps in our mechanistic understanding, and reveals the AhR signaling pathway as a novel drug target to control cell proliferation.