BACKGROUND: Endocannabinoid signaling plays an important role in regulating synaptic transmission in the striatum, a brain region implicated as a central node of dysfunction in autism spectrum disorder. Deficits in signaling mediated by the endocannabinoid 2-arachidonoylglycerol (2-AG) have been reported in mouse models of autism spectrum disorder, but a causal role for striatal 2-AG deficiency in phenotypes relevant to autism spectrum disorder has not been explored. METHODS: Using conditional knockout mice, we examined the electrophysiological, biochemical, and behavioral effects of 2-AG deficiency by deleting its primary synthetic enzyme, diacylglycerol lipase α (DGLα), from dopamine D1 receptor-expressing or adenosine A2a receptor-expressing medium spiny neurons (MSNs) to determine the role of 2-AG signaling in striatal direct or indirect pathways, respectively. We then used viral-mediated deletion of DGLα to study the effects of 2-AG deficiency in the ventral and dorsal striatum. RESULTS: Targeted deletion of DGLα from direct-pathway MSNs caused deficits in social interaction, excessive grooming, and decreased exploration of a novel environment. In contrast, deletion from indirect-pathway MSNs had no effect on any measure of behavior examined. Loss of 2-AG in direct-pathway MSNs also led to increased glutamatergic drive, which is consistent with a loss of retrograde feedback inhibition. Subregional DGLα deletion from the dorsal striatum produced deficits in social interaction, whereas deletion from the ventral striatum resulted in repetitive grooming. CONCLUSIONS: These data suggest a role for 2-AG deficiency in social deficits and repetitive behavior, and they demonstrate a key role for 2-AG in regulating striatal direct-pathway MSNs.