To examine time trends and the influence of socio-demographic and geographic factors on incidence of Parkinson's disease (PD) diagnosis in a large UK population- based cohort from The Health Improvement Network (THIN), a UK primary care database. All patients aged over 50 years and contributing data to THIN between January 1999 and December 2009 were extracted and the incidence rates of PD diagnoses were determined by age, gender, time period, social deprivation score and urban/rural status. The overall incidence of PD diagnosis for people over 50 years was 84 per 100,000 person years (95 % CI 82-85). After accounting for socio-demographic factors, the adjusted incidence rates in men were 46 % higher (95 % CI 43-48 %) than in women. Adjusted incidence rates were also 12 % higher in urban than rural areas (95 % CI 4-20 %) and slightly lower in less socially deprived areas. Over time there was a downward trend in PD diagnosis with the adjusted incidence rates declining by around 6 % every calendar year (95 % CI 5-6 %) between 1999 and 2009. Broadening the definition of PD from diagnostic codes to include symptoms and antiparkinsonian drug prescriptions increased the overall incidence to 118 per 100,000 person years (95 % CI 116-120) and showed a much weaker downward trend over time of around 1 % per calendar year (95 % CI 1-2 %). With the broader definition, the adjusted incidence rates remained significantly higher in men compared to women and in urban areas compared with rural areas but not in socially deprived areas. The PD diagnosis rates in the primary care setting were, as expected, higher in men, and slightly higher in urban areas, but not different between socio-economic groups. There was a decline in PD diagnosis in the primary care setting, which may largely represent changes in diagnosis and/or coding rather than a true decline in incidence. © Springer-Verlag Berlin Heidelberg 2012.