This study assessed the reliability and validity of the Guidelines for Stalking Assessment and Management (SAM), a structured professional judgment measure for assessing stalking risks. The SAM was completed retrospectively from file review for 146 adult stalkers (90.4% male) referred to a community-based forensic mental health service. Interrater reliability (IRR) was initially poor, but developing a strict definition of stalking currency and rescoring the SAM led to improvement. Based on the updated scoring, IRR was moderate for judgments about whether stalking was ongoing at the time of assessment, and fair to moderate for summary risk judgments. Both case prioritization (area under the curve [AUC] = .69) and risk for continued stalking (AUC = .76) ratings discriminated between groups, with high-risk stalkers 5−9 times as likely as low-risk stalkers to reoffend by stalking their original victims. Lifetime SAM total scores (AUC = .70) also featured moderate to good discrimination. Follow-up analyses suggested that this was driven mainly by the recent presence of risk markers and the nature of any ongoing stalking situation rather than historical or individual factors. Findings support the use of the SAM to structure risk judgments made by those with experience in assessing stalking. Current results also imply that IRR might be improved by introducing (a) a fixed definition of stalking currency and (b) usage guidelines for specific contexts.