Conditioned withdrawal behavior was characterized in the pond snail Lymneae. Using light as the conditioned stimulus and high-speed orbital rotation as the unconditioned stimulus, experimental animals were trained with 30 paired presentations of light and vibration per day for 3 days. All experimental animals responded to light with withdrawal behavior. Control animals exposed to the same number of explicitly unpaired presentation of light and vibration, light alone, or no stimulation did not respond to light. Thirty paired presentations per day for 2 days resulted in a partial association of the two stimuli. Neither 45 paired presentation per day for 2 days nor 90 paired presentations for 1 day resulted in complete acquisition of the conditioned withdrawal response. The conditioned withdrawal response observed following 30 paired presentation per day for 3 to 5 days persisted to Day 10. After the conditioned withdrawal response was extinguished, only 2 to 5 paired presentation of light and vibration were required for reacquisition for most animals. This study further establishes Lymneae as an animal model of basic associative learning.