In a time of worldwide availability of annual age-specific mortality data, we lack basic tools for detecting and graphing, from a comparative perspective, fine-grained deviations from mortality trends. We provide a new age–period–cohort-based methodology, combining information from age-period (AP) and APC-detrended (APCD) analyses to detect all-cause mortality increases. Plotting the resulting AP coefficients and APCD residuals in equilateral Lexis diagrams, mortality patterns can easily be distinguished as age, period or cohort trends and fluctuations. We highlight abnormalities as interactions of age and period (‘Black Holes’). They then investigate the Black Holes of mortality of young-adult cohorts in the early 1990s in Spain, other southern European countries, and the U.S., in emphasizing their simultaneously occurring mortality crises. Additional analyses with WHO mortality data and epidemiological evidence from other studies show that these mortality increases likely result from lack of treatment and inadequate public health responses to the beginnings of the HIV/AIDS epidemic. The authors discuss other possible applications of the new method.