With increasing duration of a relationship the probability that customers experience specifically negative interaction episodes but also very positive interaction episodes increases. A key question that has not been investigated in the literature concerns the impact of these extreme interaction experiences, referred to as Critical Incidents (CIs) on the quality and strength of consumer-firm relationships. In a sample of customers in a service setting we first demonstrate that indeed the number of negative (positive) CIs possess a negative (positive) and asymmetric impact on measures of relationship quality (satisfaction, trust) and measure of relationship strength (loyalty). Second using a MIMIC approach we further shed light on the question which particular incidents are really critical for a customer firm relationship and which have to be prevented with priority.