Identifying and addressing the psychosocial needs and psychological distress of primary caregivers of children and adolescents with cancers is emerging globally as a component that should be incorporated into quality cancer care. The objective of this study was to describe the psychosocial needs, psychological distress, knowledge of caregiving, and associated factors among the primary caregivers of children and adolescents with cancers attending the leading cancer treatment center in Sri Lanka. A descriptive cross-sectional study was conducted among childhood cancer caregivers in the early post-diagnosis stage using a needs and knowledge assessment questionnaire and General Health Questionnaire-30. Associations were sought between variables by bivariate analysis and further multivariate analysis. Consecutively, emotional needs, financial needs, informational needs, practical needs, and need for family and social support were at the top of the unmet needs list. All study participants had at least one item of unmet psychosocial needs. A lower education level was significantly associated with higher unmet psychosocial needs (OR=4.990; CI=1.96-12.72). Almost all the primary caregivers were psychologically distressed (97.6 %; CI = 95.3% - 99.9%) during the early post-diagnosis period. Only 18% of caregivers had a good overall knowledge of childhood cancer caregiving. Good overall knowledge of childhood cancer caregiving was associated with low distress levels (OR =2.46; 95% CI= 1.04 – 5.83). Almost all primary caregivers of children and adolescents with cancers at the early stages of diagnosis were highly distressed and had multiple unmet psychosocial needs with poor awareness of caregiving.