(1) Background: Adolescents and young adults (AYAs) who have been diagnosed with and treated for cancer have unique healthcare needs, but more research is needed to inform developmentally targeted cancer care for this population. The purpose of the current analyses was to describe the physical and psychosocial concerns and experiences of AYA cancer survivors during the post-treatment phase. (2) Methods: A national survey was conducted by the Canadian Partnership Against Cancer to evaluate the experiences and unmet needs of cancer survivors (≥18 years) within the first 5 years following cancer treatment. The current analyses were conducted on the AYA survivor population (18–34 years). (3) Results: A total of 575 surveys were completed by AYAs. Of these, 61% were female, 51% were married/partnered, and 52% were 1–3 years post treatment. Approximately three-quarters report their physical or emotional health as good/very good. Overall, 88% reported at least one physical concern [mean of 3.98+2.11 physical concerns (range 0–9)], 90% reported at least one emotional concern [mean of 3.77+1.75 emotional concern (range 0–6)], and 79% reported at least one practical challenge [mean of 2.39+1.28 practical concerns (range 0–5)]. The most common concerns were anxiety/worry about cancer returning (83%), fatigue/tiredness (78%), and depression/loss of interest in daily activities (66%). On average, 43% of those reporting a concern sought help. Common reasons for not seeking help included not wanting to ask, being told that it was normal to feel the way they did, or embarrassment. Of those who did seek help, 37% encountered difficulty obtaining assistance. (4) Conclusions: These results suggest that post-treatment AYA cancer survivors have a high rate and number of physical, psychosocial, and practical concerns and are often not seeking or receiving help to address these. Proactive approaches to characterizing and eliminating barriers to obtaining appropriate care are needed.