Diagnosis of Autism Spectrum Disorders (ASD) is complex and parents worldwide often experience difficulties and frustration during the diagnostic process. This study examined the duration of the diagnostic period, the number of professionals consulted, the relationship with the professional(s) and the perceived helpfulness of information provided in relation to how they impact on parental satisfaction and stress during the diagnostic process. The study also obtained professional perspectives regarding current diagnostic practices to understand aspects of the process which may be helpful in increasing professional confidence in diagnosing ASD. One hundred and two parents of 2–17 years old children and young people with ASD recruited from ASD special schools, intervention centres and hospitals in Singapore completed a survey, which included information on various aspects of the diagnostic process and measures of autism severity, parental stress and satisfaction. Seventeen professionals completed a similar survey. Parents from higher educational and socioeconomic backgrounds were more likely to raise concerns about their child's development at an earlier age. Higher parental stress was associated with more professionals consulted and lower perceived collaboration with professionals. Higher parental satisfaction was associated with higher perceived collaboration with professionals, higher perceived helpfulness of received information, lower severity of child ASD symptoms and lower levels of stress. Findings are discussed in relation to clinical practice guidelines and existing literature on the process and impact of diagnosis on families.