Cool soil conditions after planting frequently delay corn (Zea Mays L.) emergence in the northeastern USA, which is conducive to seed corn maggot [Hylemyia platura (Delia platura)] damage.  Two corn hybrids with three seed-applied insecticide treatments, which included a control, 0.25 mg a.i. seed^-1 clothianidin [(E) 1-(2-chloro-1,3-thiazol-5-ymethyl)-3-methyl-2-nitroguanidine], and 1.25 mg a.i. seed^-1 clothianidin were evaluated in 2004 and 2005 in New York to determine how clothianidin affects leaf area index (LAI), mean crop growth rate (CGR), grain yield, and harvest index (HI).  Both clothianidin treatments had greater LAI (~2.60) at the 10^th-11^th leaf stage (V10-11) compared with the control (2.45) but differences did not exist at the silking (R1) stage (4.30-4.45).  Both clothianidin treatments compared with the control had similar CGR from the V10-11 to R1 stage (~34 g m^-2d^-1) and from the R1 stage to silage harvest (~25 g m^-1d^-1).  Both clothianidin treatments also had similar grain yield (9.7 – 10.3 Mg ha^-1) and HI values (~0.52) compared with the control (10.2 and 0.54, respectively).  Grain yield had significant negative correlations in 2005 with plant densities (-0.82), LAI at the V11 and R1 stages (-0.87), and CGR from V11 to the R1 stage (-0.78) probably because of hot and dry growing conditions, especially during the 10-20 d period after silking.  Based on the results of this study, we do not recommend clothianidin seed treatments on grain corn when following soybeans in the northeastern USA.