Parkinson’s disease (PD) is a common movement disorder characterized by motor symptoms such as bradykinesia, rigidity, and tremor. It is also associated with non-motor symptoms. The disease typically begins in people aged 65–70 years, with less than 5% of cases occurring before the age of 40. Genetic factors are involved in 5–10% of cases, though monogenetic forms are rare in unselected populations. PD is slightly more common in men than women. The prevalence of PD is generally accepted to range from 100 to 200 per 100,000 people, with an annual incidence of about 15 per 100,000. There is ongoing debate about whether PD is increasing in prevalence, possibly due to an aging population. PD was first described by James Parkinson in 1817. It is characterized neuropathologically by α-synuclein-containing Lewy bodies in the substantia nigra, leading to the loss of dopaminergic neurons and reduced voluntary movement facilitation. As the disease progresses, Lewy body pathology spreads to other brain regions. Non-motor symptoms have gained increasing attention and are now included in diagnostic criteria. The diagnostic criteria for PD have been revised to include supportive criteria, absolute exclusion criteria, and red flags. A diagnosis of "clinically established PD" requires at least two supportive criteria, the absence of absolute exclusion criteria, and no red flags. The revised criteria aim to improve diagnostic accuracy and ensure better concordance between clinical diagnosis and neuropathological confirmation. Epidemiological studies show that PD is rare before the age of 50, with a prevalence of 4% in the highest age groups. Incidence varies widely, with annual rates ranging from less than 10 to more than 20 per 100,000. Incidence studies may be affected by under-diagnosis, especially in the elderly. In the Nordic countries, the incidence is around 13.5 per 100,000, with most cases occurring in people over 50. Early-onset PD is rare in population-based studies, with only 4% of patients developing cardinal signs before the age of 50.Parkinson’s disease (PD) is a common movement disorder characterized by motor symptoms such as bradykinesia, rigidity, and tremor. It is also associated with non-motor symptoms. The disease typically begins in people aged 65–70 years, with less than 5% of cases occurring before the age of 40. Genetic factors are involved in 5–10% of cases, though monogenetic forms are rare in unselected populations. PD is slightly more common in men than women. The prevalence of PD is generally accepted to range from 100 to 200 per 100,000 people, with an annual incidence of about 15 per 100,000. There is ongoing debate about whether PD is increasing in prevalence, possibly due to an aging population. PD was first described by James Parkinson in 1817. It is characterized neuropathologically by α-synuclein-containing Lewy bodies in the substantia nigra, leading to the loss of dopaminergic neurons and reduced voluntary movement facilitation. As the disease progresses, Lewy body pathology spreads to other brain regions. Non-motor symptoms have gained increasing attention and are now included in diagnostic criteria. The diagnostic criteria for PD have been revised to include supportive criteria, absolute exclusion criteria, and red flags. A diagnosis of "clinically established PD" requires at least two supportive criteria, the absence of absolute exclusion criteria, and no red flags. The revised criteria aim to improve diagnostic accuracy and ensure better concordance between clinical diagnosis and neuropathological confirmation. Epidemiological studies show that PD is rare before the age of 50, with a prevalence of 4% in the highest age groups. Incidence varies widely, with annual rates ranging from less than 10 to more than 20 per 100,000. Incidence studies may be affected by under-diagnosis, especially in the elderly. In the Nordic countries, the incidence is around 13.5 per 100,000, with most cases occurring in people over 50. Early-onset PD is rare in population-based studies, with only 4% of patients developing cardinal signs before the age of 50.