In this grounded, dimensional analysis we describe the experiences of five couples whose infants had equivocal diagnostic test results following positive genetic newborn screens for cystic fibrosis. We analyzed interview data collected at two points during each infant's first year. Uncertainty emerged as the central thematic dimension. Results showed that parents passed through a series of stages similar to the process described in Mishel's Uncertainty in Illness Theory (UIT), thus extending the application of the theory to circumstances in which the very presence of an illness is uncertain. Findings informed a modified version of the UIT comprised of five domains: stimuli frame, degree of uncertainty, opportunity- danger continuum, affective responses, and coping. This model incorporates Morse's conception of suffering. Three contextual domains influenced parents' experiences at various junctures along the uncertainty trajectory: individual characteristics, structure providers, and time. We discuss implications of the model for future research and clinical practice relative to genetic testing.