This paper proposes that courts should not grant prison officials' motions for summary judgment on the ground that the inmate-plaintiff has not shown that the officials knew of the risk, if the plaintiff has shown the existence of conditions at the institution that would make obvious the existence of a substantial risk of sexual assault. This approach would be more faithful to recent U.S. Supreme Court rulings on prison conditions and the established law on summary judgment. More importantly, it would induce prison officials who want to avoid liability for inmate assaults to take the steps necessary to create a reasonably safe prison environment. Part I of this paper examines the problem of sexual assault in America's prisons and jails, including the institutional conditions that facilitate its occurrence and its effects on inmates. Part II discusses the U.S. Supreme Court's holding that plaintiff-inmates must show that defendant-officials acted with "deliberate indifference," and how lower courts have applied and misapplied this holding in deciding whether the plaintiffs have adduced sufficient evidence of the official's "actual knowledge" of the risk to survive a motion for summary judgment. Part III concludes that lower courts should not grant summary judgment to defendant-officials if the plaintiff-inmate has shown that the risk of assault was obvious, and it considers ways that an inmate could make this showing. 158 footnotes