Parkinson's Disease (PD) is a progressive and incurable neurological disorder which affects approximately 1% of people over 65. Despite the relatively high prevalence of PD, there has been very little research exploring the lived experience of people who suffer from this illness. In this study 9 people with PD were interviewed with their partner about their experiences of being diagnosed with PD. The qualitative methodology of grounded theory was then used to produce an analytical version of their accounts. The transitional model of psychological adjustment to PD developed from the analysis consisted of four phases: pre-diagnosis, diagnosis, initial adjustment and transition to the chronic phase. The individual experience of this model was mediated by five sets of factors: age-related issues, professional support, family and social context, past and current health status and the context of daily life. The pre-diagnosis phase consisted of four stages: noticing and discounting or rationalising; suspecting; deciding to seek medical help and searching for a medical diagnosis. Receiving a diagnosis was, most commonly, responded to with intense emotional shock related to the uncertainty of what the diagnosis meant for future life. The aim of the initial adjustment phase was to reduce uncertainty, re-establish a sense of control and cope with the emotional response to the diagnosis. Analysis suggested that participants engaged in three major tasks of adjustment to achieve these aims: information seeking, resolving identity dilemmas and coping with symptoms and treatment demands. Each person's approach to these tasks was determined by the way in which they conceptualised PD within the context of daily life. Four patterns of conceptualisation were identified: PD as irrelevant, an interruption, something to be integrated into current lifestyle or an intrusion. Transition to the chronic phase of illness was characterised by the person having found ways to live with continued uncertainty, having found personal meaning in the diagnosis and a reduction in emotional distress. The theoretical and clinical implications of the findings are discussed and limitations of the study considered.