Velvet lupine (Lupinus leucophyllus Dougl. ex Lindl) contains the teratogenic alkaloid anagyrine that causes a crooked calf syndrome. An outbreak of crooked calves occurred in the Channeled Scabland region of eastern Washington in 1997 following 2 years of above-average precipitation. Following this catastrophic loss, we began studies to track velvet lupine density and relate its population cycle to precipitation. In the first study, five 1-m² quadrats were systematically placed in dense lupine patches at each of 5 locations throughout the scabland region. The quadrats were permanently marked and the number of seedlings and established mature plants were counted biweekly or monthly through the growing seasons of 2001–2005. In the second study, four 1 × 30-m belt transects were established at each of 3 additional locations in the scabland region. The number of seedlings and mature lupine plants were counted within these transects in June or July each year from 2002 to 2009. A third study was conducted to determine the slope or aspect where lupine was most abundant. Ten sites were located along the Cow Creek drainage which runs through the region. At each site, 1 × 10-m belt transects were established in alluvial bottoms, slopes, and shallow rocky ridges. In study 1, density of mature lupine plants generally declined between 2001 and 2005 (P < 0.001) and was correlated with spring precipitation (r = 0.77). In study 2, density of mature lupine plants differed between years (P < 0.001), declining from 2002 through 2005 but increasing in 2007 in response to heavy precipitation the previous fall and spring (mature lupine plants vs. fall precipitation, r = 0.75; and mature lupine plants vs. spring precipitation, r = 0.62). Density of lupine was greatest on slopes (2.6 plants · m^-2), intermediate on alluvial bottoms (1.5 plants · m^-2), and lowest on shallow rocky ridges (0.26 plants · m^-2). Velvet lupine populations appear to cycle with climatic patterns, increasing following wet years and dying back in drought.