Erlotinib is increasingly being used for the treatment of non-small cell lung cancer. The recommended dose is 150 mg/day and no efficacy data is available for lower doses. We describe a case of dramatic tumor response to 50 mg erlotinib in a patient with EGFR mutation positive NSCLC who developed a severe rash on full dose erlotinib. Rash is known to correlate with response and survival in patients treated with erlotinib. Our case suggests that in the presence of rash, dose reductions to "subtherapeutic" levels remain effective and may prevent unnecessary early treatment termination.