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The medial orbitofrontal cortex (mOFC) regulates a variety of cognitive functions, including refining action selection involving reward uncertainty. This region sends projections to numerous subcortical targets, including the ventral and dorsal striatum, yet how these corticostriatal circuits differentially regulate risk/reward decision-making is unknown. The present study examined the contribution of mOFC circuits linking the nucleus accumbens (NAc) and dorsomedial striatum (DMS) to risk/reward decision-making using pharmacological disconnections. Male rats were well trained on a probabilistic discounting task involving choice between small/certain or large/risky rewards, with the probability of obtaining the larger reward decreasing or increasing over a session. Disconnection of mOFC-striatal pathways was achieved using infusions of GABA agonists inactivating the mOFC in one hemisphere, combined with NAc or DMS inactivation in the contralateral or ipsilateral hemisphere. Perturbing mOFC → NAc circuits induced suboptimal, near-random patterns of choice that manifested as a flattening of the discounting curve. Animals were equally likely to stay or shift following rewarded/nonrewarded choices, suggesting this pathway mediates use of information about reward history to stabilize decision biases. In contrast, mOFC → DMS disconnection impaired adjustments in decision biases, causing opposing changes in risky choice depending on how probabilities varied over time. This was driven by alterations in lose-shift behavior, suggesting mOFC → DMS circuits track volatility in nonrewarded actions to adjust choice in accordance with changes in profitability. Thus, separate mOFC-striatal projection pathways regulate dissociable processes underlying decision-making, with mOFC → NAc circuits aiding in establishing and stabilizing tasks states and mOFC → DMS circuits facilitating transitions across states to promote flexible reward seeking.SIGNIFICANCE STATEMENTThe medial orbitofrontal cortex regulates a variety of goal-directed behaviors, yet the functional circuits through which it mediates higher order decision-making functions are unclear. The present study revealed that different mOFC projection pathways facilitate diverse aspects of decision-making involving risks and rewards by engaging separate networks of neurons that interface with distinct ventral and dorsal striatal targets. These findings clarify some of the normal functions of these corticostriatal pathways and may have implications for understanding how dysfunction in these circuits relate to certain psychiatric disorders.