TCanvas *c1 = new TCanvas("c1","hists with different scales",600,400);

gStyle->SetOptStat(kFALSE);
TH1F *h1 = new TH1F("h1","my histogram",100,-3,3);
Int_t i;
for (i=0;i<10000;i++) h1->Fill(gRandom->Gaus(0,1));
h1->Draw();
c1->Update();

TH1F *hint1 = new TH1F("hint1","h1 bins integral",100,-3,3);
Float_t sum = 0;
for (i=1;i<=100;i++) {
   sum += h1->GetBinContent(i);
   hint1->SetBinContent(i,sum);
}

Float_t rightmax = 1.1*hint1->GetMaximum();
Float_t scale = gPad->GetUymax()/rightmax;
hint1->SetLineColor(kRed);
hint1->Scale(scale);
hint1->Draw("same");

TGaxis *axis = new TGaxis(gPad->GetUxmax(),gPad->GetUymin(),
      gPad->GetUxmax(), gPad->GetUymax(),0,rightmax,510,"+L");
axis->SetLineColor(kRed);
axis->SetLabelColor(kRed);
axis->Draw();

gROOT->GetListOfCanvases()->Draw()