Psittacosis is a disease that can be transmitted from birds to humans and is caused by the intracellular bacterium Chlamydia psittaci. C. psittaci has been detected in more than 465 bird species and can cause clinical signs ranging from no symptoms to more severe symptoms such as conjunctivitis and pneumonia to liver failure and death. In humans, infection with C. psittaci can result in a flu-like illness and severe pneumonia, sometimes requiring hospitalisation. In the Netherlands, the disease is notifiable in humans and pet birds (except poultry). The number of human (40-70 per year) and veterinary (60-110 per year) notifications has been stable in recent years, but in 2019 there was a small increase in the number of human cases (91). The Netherlands Food and Consumer Product Safety Authority (NVWA) is responsible for the control in birds in the Netherlands, meaning the NVWA receives the notifications and carries out sampling. The owner of the birds is responsible for contacting a veterinarian to prescribe an antibiotic treatment. Two weeks after the treatment birds are retested. After treatment, birds regularly test positive with PCR, but the cause of these positive retests is unknown. In this report, existing NVWA dossiers were analysed to investigate which factors are associated with a positive retest after treatment. In total, 79 cases could be further analysed, of which 38 tested positive after the first treatment. Factors related to outdoor housing, possible outdoor contact and density appeared to be associated with a positive retest, although no strong relation was found. Additional research would be needed to confirm this relationship. In the data set, a large part of possible risk factors was missing, such as information related to treatment, housing, cleaning and disinfection. These factors could not be analysed. In addition, an improved treatment protocol for field cases was written based on existing literature. This protocol was used in one field case (autumn 2019). During this case study, it turned out that strict cleaning and disinfection is very difficult under field conditions. The analysis of the NVWA dossiers and the case study confirmed that bird husbandries are very diverse, with different types of housing and bird species. In addition, PCR results are sometimes difficult to interpret, as the presence of DNA is detected and not infectious C. psittaci bacteria, which requires a case-dependent approach. Overall, tailor-made advice is probably key in the control of psittacosis in pet birds. This report is the result of a research project within the statutory tasks of Wageningen Bioveterinary Research. This project aimed to improve the current control of psittacosis by evaluating information from available NVWA dossiers and systematically following up a number of field cases. In addition, antibiotic residues in bird feces were investigated. This information is not included in this report but will be reported to the Ministry of Agriculture, Nature and Food Quality via the usual reports.