Fatal intoxications are common in a medico-legal autopsy setting and are associated with sparse findings during autopsy. It has been suggested that an increased lung weight may be associated with such fatalities. Previous literature is generally limited to a descriptive approach, including only opioid deaths, and lacking a definition of "heavy" lungs. Our aim was to create a model to identify cases with heavy lungs and to assess the predictive power of "heavy" lungs in identifying cases of different types of fatal intoxications during autopsy in an unselected medico-legal autopsy population. We identified all medico-legal autopsy cases ≥18 years in Sweden from 2000 through 2013. The lung weight to heart weight (LWHW) ratio was calculated. The positive predictive values (PPV) and negative predictive values (NPV) of both lung weight and LWHW ratio were calculated. Mean lung weight was higher in the intoxication group but the predictive power in the individual case was limited. Lung weight to heart weight ratio had better predictive power than lung weight alone, with a PPV of at most 0.15(0.14, 0.16 95% CI), while the NPV was 0.96 (0.95, 0.96 95% CI). The association between fatal intoxication and increased lung weight was positive, regardless of method and cutoffs used. While the PPV was poor, the NPV could reduce suspicion of fatal intoxication in the absence of other information. LHWH ratio is only a probability factor for fatal intoxication; accurate cause of death determination-as always-requires consideration of circumstances, autopsy, and toxicologic findings.