OBJECTIVES: To compare effectiveness and costs of personal reminder approaches (mailed vs. phone) to improve dilated fundus examination (DFE) follow-up adherence in patients with diabetes.   METHODS: In a prospective trial, 356 diabetics due for DFE were randomly assigned to usual care (UC; reference case), mailed intervention (MI), or telephone intervention (TI). UC (n=119) received a standard form letter. MI (n=117) received a personalized letter encouraging scheduling of eye examination with an educational brochure about diabetic eye disease. TI (n=120) received personal calls (up to 3 attempts) to schedule a follow-up with standard form letter. The primary outcome was DFE within 90 days of suggested return. Costs ($US 2013) included time costs (staff time in preparing letters, conducting calls, and documentation converted to dollars using wages + benefit costs), phone charges, supplies, and postage. Since TI dominated MI, univariate sensitivity analysis examined the impact of reducing phone costs. RESULTS: Participants were mostly female (66%) and African-American (70%) with a mean age of 61 years. TI were more likely to schedule DFE (65% vs. 42%; RR1.54; CI1.20-1.96; p<0.001) vs. UC. DFE within 90 days of suggested return in TI was also significantly higher than UC (51% vs. 36%, RR1.41; CI1.05-1.89; p=0.024). MI were slightly less likely to schedule DFE vs. UC (38% vs. 42%, RR0.90; CI0.66-1.22; p=NSS) and attend DFE (32% vs. 36%; RR0.90; CI 0.63-1.28; p=NSS). The total cost of TI was $603.98 or $5.03/participant and the cost/follow-up DFE was $26.05. Sensitivity analyses revealed that the cost/follow-up can be greatly reduced but remains additional vs. UC ($2.76 if $0.25/call, $11.13 if $1/call; $22.29 if $2/call).  CONCLUSIONS: Personal phone assistance in scheduling DFE follow-up assistance is more effective but also more costly. Follow-up research has been initiated to determine whether automated phone reminders can achieve similar effectiveness at a lower cost.