Background Cutaneous basal cell carcinomas (BCCs) and squamous cell carcinomas (SCCs) have poorer outcomes if treated when large. Objective We sought to estimate the growth rate of BCCs and SCCs and examine the relationship of personal, pathway, and cancer factors with cancer size (diameter). Methods We surveyed patients, pathology, and treatment for invasive BCCs and SCCs in 1 Australian region in 2000 through 2001. Results BCC size increased with increasing time since first noticed. Relative to mean size at 0 to 2 months, the mean size ratio was 1.10 at 2 to 8 months and increased steadily to 1.81 at 5 to 10 years (P <.001). Few BCCs were untreated beyond 10 years. There was no consistent evidence that SCC size increased with increasing time. Larger BCCs were independently associated with older age, male sex, no skin checks by a physician, aggressive tumor type, ulceration and lesion-associated scar tissue, and larger SCCs with male sex, skin checks by a physician every 1 to 3 months, and location on limbs. Limitations Patient recall of dates and lack of thickness for SCCs are limitations. Conclusion Earlier diagnosis of BCCs, perhaps through skin checks by a physician, may reduce their size and improve outcome. SCC size did not evidently increase with time.